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).

"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."

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

"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?

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.

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.