Dr. Glen MacPherson doesn’t remember the first time he heard the sound. It may have started at the beginning of 2012, a dull, steady droning like that of a diesel engine idling down the street from his house in the Sunshine Coast of British Columbia. A lecturer at the University of British Columbia and high school teacher of physics, mathematics and biology, months passed before MacPherson realized that the noise, which he’d previously dismissed as some background nuisance like car traffic or an airplane passing overhead, was something abnormal.

“Once I realized that this wasn’t simply the ambient noise of living in my little corner of the world, I went through the typical stages and steps to try to isolate the sources,” MacPherson told Mic. “I assumed it may be an electrical problem, so I shut off the mains to the entire house. It got louder. I went driving around my neighborhood looking for the source, and I noticed it was louder at night.”

Exasperated, MacPherson turned his focus to scientific literature and pored over reports of the mysterious noise before coming across an article by University of Oklahoma geophysicist David Deming in the Journal of Scientific Exploration, a peer-reviewed academic journal devoted to exploring topics outside of mainstream science. “I almost dropped my laptop,” says MacPherson. “I was sure that I was hearing the Hum.”

“The Hum” refers to a mysterious sound heard in places around the world by a small fraction of a local population. It’s characterized by a persistent and invasive low-frequency rumbling or droning noise often accompanied by vibrations. While reports of “unidentified humming sounds” pop up in scientific literature dating back to the 1830s, modern manifestations of the contemporary hum have been widely reported by national media in the United Kingdom, the United States and Australia since the early 1970s.

Regional experiences of the phenomenon vary, and the Hum is often prefixed with the region where the problem centers, like the “Windsor Hum” in Ontario, Canada, the “Taos Hum” in New Mexico, or the “Auckland Hum” for Auckland, New Zealand. Somewhere between 2 and 10% of people can hear the Hum, and inside isolation is no escape. Most sufferers find the noise to be more disturbing indoors and at night. Much to their dismay, the source of the mysterious humming is virtually untraceable.

While the uneven experience of the Hum in local populations has led some researchers to dismiss it as a “mass delusion,” the nuisance and pain associated with the phenomenon make delusion a dissatisfying hypothesis. Intrigued by the mysterious noise, MacPherson launched The World Hum Map and Database in December 2012 to collect testimonies of other Hum sufferers and track its global impact (he now also moderates a decade-old Yahoo forum along with Deming).

MacPherson quickly discovered that what to him was a strange rumbling was actually having pernicious effects on hundreds of people, from headaches to irritability to sleep deprivation. There are reports that weeks of insomnia caused by the Bristol Hum drove at least three U.K. residents to suicide. “It completely drains energy, causing stress and loss of sleep,” a sufferer told a British newspaper in 1992. “I have been on tranquilizers and have lost count of the number of nights I have spent holding my head in my hands, crying and crying.” Thousands of people around the world have shared similar experiences of the Hum; some, like MacPherson, are devoting their time to finally uncovering its source.

Above: Self-reported experiences of the Hum, recorded as part of The World Hum Map and Database by Glen MacPhearson, British Columbia.

Tom Moir, a professor at the Auckland University of Technology and Hum investigator, first started looking into the Hum after an Auckland resident called Moir’s office at Massey University in 2002. Moir, a professor of control engineering, placed an ad in the local paper after receiving a visit from a Hum sufferer who desperately wanted to find the source of the racket. He received dozens of responses within days, all describing a mysterious droning noise matching the one described in Deming’s landmark paper. Residents of Auckland’s northern shore claimed that the Hum was so intense that it was preventing them from sleeping or concentrating. “When it’s loud, it’s like there’s vibrations between your ears, that your brain is vibrating,” one resident told local TV in 2011. Another Auckland resident said that the noise had been so disruptive to his life that he’d deafened himself in one ear with a chainsaw so he could sleep through the night. Many had lived a life of vibroacoustic agony, unsure if what they were hearing was real or not.

“For my entire life, I was a perfect sleeper,” says Steve Kohlhase, 60, who first started to experience the Hum at night in his Brookfield, Connecticut home in September 2009. A mechanical engineer in the chemical industry, Kohlhase, like so many other Hum sufferers, has devoted his free time to searching for the source of the noise. “I immediately felt the effects in my head: It feels like your fingers are in your ears. Other people have different experiences: Sometimes the floorboards in the house have a distinct vibration to them, or they they feel it in their feet in their bedsprings. Many people find their ears ringing.”

Above: “The Torment of the Hum” by Rosemarie Mann (2004).

So what’s behind the Hum? After nearly four decades, Hum investigators may finally have some idea. The general consensus among sufferers is that the Hum is comprised of very low frequency (or ‘VLF’, in the range of 3 kHz to 30 kHz and wavelengths from 10 to 100 kilometers) or extremely low frequency (or ‘ELF’, in the range of 3 to 30 Hz, and corresponding wavelengths from 100,000 to 10,000 kilometers) radio waves, which can penetrate buildings and travel over tremendous distances.

Both ELF and VLF waves have been shown to have potentially adverse affects on the human body. While the common refrain about ELF radiation in popular culture normally involves your cell phone giving you cancer, research by the World Health Organization and the Institute for Electrical and Electronics Engineers has shown that external ELF magnetic fields can induce currents in the body which, at very high field strengths, cause nerve and muscle stimulation and changes in nerve cell excitability in the central nervous system. And VLF waves, like other low-frequency electromagnetic radiation, have also been shown to have a direct impact on biological functions

Finally, there’s a body of empirical evidence that makes this theory more appealing. A study funded by the Canadian government and led by University of Windsor mechanical engineering professor Dr. Colin Novak spent the last year listening to the “Windsor Hum” that’s been torturing residents in the Windsor area of Ontario since 2011. A previous study had confirmed the existence of the low frequency noise in the vicinity of Zug Island, a highly industrialized island located on Michigan side of the Detroit River. The researchers used specialized equipment to capture and develop a sonic “fingerprint” of the mysterious sound. The study concluded that not only does the Windsor Hum actually exist, but its likely source was a blast furnace at the U.S. Steel plant on Zug Island, which reportedly generates a high volume of VLF waves during its hours of operation. “It sounds like a large truck or a train locomotive is parked outside your house, buzzing away, causing the windows to shake,” Novak, himself a Hum sufferer, told Canada’s CTV News. “It can be quite uncomfortable at times.”

“I have been on tranquilizers and have lost count of the number of nights I have spent holding my head in my hands, crying and crying.”

Dr. Novak’s study caps off decades of Hum theories, but given the inconsistent experience of the phenomenon around the world, cataloguers of the Hum still aren’t quite sure if it has a single, definitive source. While ELF and VLF waves may cause people to experience the incessant droning, not every local Hum appears to have an easily traceable source. What about the Aukland and Taos Hums? And why does the Hum seem to appear and disappear for months at a time?

Some Hum investigators suspect that there’s a global source responsible for the Hum worldwide. Deming’s research, considered close to authoritative in the Hum community, suggests that evidence of the Hum corresponds with an accidental, biological consequence of the “Take Charge and Move Out” (TACAMO) system adopted by the US Navy in the 1960s as a way for military leaders to maintain communications with the nation’s ballistic missile submarines, land-based intercontinental ballistic missiles, and long-range bombers during a nuclear war. As part of TACAMO, military aircraft use VLF radio waves to send instructions to submarines: Because of their large wavelengths, VLF can diffract around large obstacles like mountains and buildings, propagate around the globe using the Earth’s ionosphere and penetrate seawater to a depth of almost 40 meters, making them ideal for one-way communication with subs. And VLF, like other low-frequency electromagnetic waves, have been shown to have a direct impact on biological functions. (Strategic Communications Wing One at Tinker Air Force Base in Oklahoma, which is responsible for the manning, training and equipping of aircraft utilized as part of the TACAMO system, did not respond to requests for comment.)

And there are other theories. While Moir agrees with MacPherson that the disturbance is occurring at a very low frequency, he’s convinced that the source of the Auckland Hum is primarily acoustic rather than electromagnetic, partially because he claims his research team has managed to capture a recording of the Hum.

Listen: An alleged recording of the Auckland Hum by Prof. Tom Moir. Plug in your headphones or increase the volume of your speaker system to maximum to hear.

Listen: A simulation of the Auckland Hum created by a research team lead by Prof. Tom Moir.

“It’s a very, very low wavelength noise, perhaps between 50 or 56 Hz,” Moir told Mic. “And it’s extremely difficult to stop infrasound because it can have a wavelength of up to 10 meters, and you’d need around 2.5 meter thick walls, built with normal materials, to keep it out. It gets into our wooden houses very easily. And part of the reason people have so much trouble identifying the source of it is because of how low frequency the Hum is: It literally moves right through your head before you can figure out which ear picked it up first.”

This isn’t to say that an electromagnetic explanation is impossible: There could be both electromagnetic or acoustic sources that complement each other. The real difficulty is separating the two hypotheses through testing. “There haven’t been tests done were you subject people to these frequencies and put them in an anechoic chamber,” says Moir, referring to rooms designed to completely absorb reflections of either sound or electromagnetic waves. “But until you can actually prove that by doing tests, there’s no way to firmly come to that conclusion.”

These tests can’t come soon enough for Steve Kohlhase, the mechanical engineer hunting for the Hum in Connecticut. Kohlhase, like Dr. Novak and the researchers who traced the Windsor Hum to Zug Island, hypothesizes that the source of the Connecticut Hum is industrial rather than military, generated by a network of nearby high volume gas pipelines. The arrival of the Hum, Kohlhase argues, coincided with increased development of natural gas pipelines in northern Fairfield County, and the increased hydraulic pressure used by the Iroquois and Algonquin interstate pipelines that run through his corner of Connecticut could result in the non-directional, extremely low frequency (ELF) humming noise previously unheard in the region.

This a pressing public health issue. It is not just some casual annoyance, claims Kohlhase. The resulting infrasonic sounds blanketing the region could result in widespread vibroacoustic disease — an occupational disease occurring from long-term exposure to large pressure amplitude and low frequency noise — the symptoms of which include those often described by Hum suffers: depression, mood swings, insomnia and other stress-induced pathologies.

The Hum may transition from unexplained mystery to unfortunate byproduct of modernity, a fixture of human geography like light pollution.

State and local governments may finally be paying attention. Worried about the potential behavioral effects of the Connecticut Hum, Kohlhase dispatched concerned emails to state and local health officials laying out his research. Kohlhase was so persistent that he contacted Connecticut State Police investigators almost six weeks after the shooting at Sandy Hook Elementary School in Newtown, Connecticut, insisting that the Hum allegedly produced by nearby gas pipelines could have had something to do with Adam Lanza’s behavior leading up to the shooting. While law enforcement officials field a flood of calls from conspiracy theorists and pranksters following any major incident, investigators deemed the information Kohlhase provided “appropriate” for inclusion in the 7,000 images, audio files, videos and documents released to the public.

“The reason that it could’ve affected Lanza is that sound and vibrations can have extremely subtle, detrimental affects on someone who’s fragile minded,” explains Kohlhase. “Imagine if you’re mentally ill or have a brain tumor or are just, well, fragile of mind. I am absolutely not an expert, but if sound sensitivity is such a serious issue to those on the autism spectrum, perhaps extremely low frequency sounds can result in a pernicious effect.” Kohlhase points to Aaron Alexis, the defense subcontractor who battled mental health issues and scrawled “My ELF Weapon” into the stock of his shotgun before killing 12 people at the Washington Navy Yard in 2013. “He told his psychiatrist he’d been chased by vibrations. Look at a map of instances like this, in Washington, or the Gabby Giffords shooting in Arizona, and I bet you’ll see that each place coincides with a Hum cluster.”

Here is the fundamental problem facing Hum sufferers around the world: believability. Scientific data and anecdotal experiences of the Hum vary so much from region the world that it’s still unclear whether VLF and ELF waves are the source of it, let alone a catalyst for mass murder. The idea of a mysterious noise driving people to suicide has given birth to all kinds of pseudoscientific conjecture, making the phenomenon a favorite for conspiracy junkies who suspect foul play by some malicious government scheme (or UFOs, obviously). The World Hum, a site devoted to exploring the “mysterious phenomenon being heard by thousands around the world,” is riddled with byzantine entries about UFOs crashing in Siberia.

MacPherson knows how insane it sounds. “There’s a terrible irony to the vision of a conspiracy nut in a tinfoil hat, trying to keep the government from beaming thoughts into their heads,” laughs MacPhearson, “since aluminum does protect against some electromagnetic radiation. This is why you don’t put that stuff in the microwave.”

The federally funded investigation into the Windsor Hum and the serious examination of Kohlhase’s research by Connecticut authorities may serve as a beacon of hope for Hum investigators like MacPherson, Moir, Novak and Kohlhase. State-funded tests on Hum-affected regions may yield data that could lead to a real-world solution, rather than conspiracy theories. Until then, developing a unified picture of the Hum is exactly what MacPherson wants to accomplish in British Columbia. By providing one destination for Hum data and testimony, he’s hoping that professional and independent researchers will use the collected data to help develop and execute experiments that could help identify the source of their local Hum.

But until someone funds and conducts rigorous tests in an affected region, says Moir, people will continue to use the Hum as an excuse to blame modern technology, from mobile phones to telecom towers to the digital radio bands used by law enforcement. And that aura of pseudoscientific insanity surrounding the Hum has made the job of independent researchers more challenging. “In the past, I’ve contacted my representatives, I’ve contacted my governor,” says Kohlhase. “There’s willful ignorance going on about this problem and the real consequences it has.”

But should researchers like MacPherson and Moir finally pinpoint the local sources of the pain-inducing phenomenon, the Hum may transition from unexplained mystery to unfortunate byproduct of modernity, a fixture of human geography like light pollution. In the meantime, many just want to identify some relief.

“A lot of serious researchers don’t want to have their name attached to that, but I’m not a formal academic researcher, and I’m quite willing to lend some credibility to this idea if I can,” says MacPherson. “This phenomenon is real and many people are suffering: I’m just trying to do the best I can to help.”