Sue Taylor first started hearing it at night in 2009. A retired psychiatric nurse, Taylor lives in Roslin, Scotland, a small village seven miles outside of Edinburgh. “A thick, low hum,” is how she described it, something “permeating the entire house,” keeping her awake. At first she thought it was from a nearby factory, or perhaps a generator of some kind. She began spending her evenings looking for the source, listening outside her neighbors’ homes in the early hours of the morning. She couldn’t find anything definitive. She had her hearing checked and was told it was perfect, but the noise persisted. She became dizzy and nauseous, overcome, she says, by a crushing sense of despair and hopelessness at her inability to locate or escape the sound. When things got bad, it felt to Taylor like the bed—and the whole house—was vibrating. Like her head was going to explode. Her husband, who had tinnitus, didn’t hear a thing. “People looked at me like I was mad,” she said.

Lori Steinborn lives in Tavares, Florida, outside of Orlando, and in 2006 she had started hearing a noise similar to the one Taylor was hearing. Steinborn thought it was her neighbors at first: some nearby stereo blasting, the bass coming through the walls. It would start most nights between 7 and 8 p.m. and last until the early hours of the morning. Like Taylor, she began searching for the sound; leaving town helped her get away from it, but it was waiting when she returned.

The experience described by Steinborn and Taylor, and many others, is what’s come to be known as “the Hum,” a mysterious auditory phenomenon that, by some estimates, 2 percent of the population can hear. It’s not clear when the Hum first began, or when people started noticing it, but it started drawing media attention in the 1970s, in Bristol, England. After receiving several isolated reports, the British tabloid the Sunday Mirror asked, in 1977, “Have You Heard the Hum?” Hundreds of letters came flooding in. For the most part, the reports were consistent: a low, distant rumbling, like an idling diesel engine, mostly audible at night, mostly noticeable indoors. No obvious source.

The story of the Hum begins in such places, far from the hustle and bustle of cities, where stillness blankets everything. That’s where you hear it, and that’s where it becomes intolerable. After it was first reported in Bristol, it emerged in Taos, New Mexico; Kokomo, Indiana; Largs, Scotland. A small city newspaper would publish a report of a local person suffering from an unidentified noise, followed by a torrent of letters to the editor with similar complaints.

Sometimes, this would lead to a begrudging official investigation, but these nearly always ended inconclusively. Far more likely was widespread dismissal of the complaints, which made the experience that much more frustrating for those who heard the Hum. Though University of Southampton researchers R.N. Vasudevan and Colin G. Gordon, who investigated claims of the Hum in 1977, established that it was “very probably” a real phenomenon and not an auditory hallucination, Hum sufferers have been consistently written off as either delusional or simply suffering from tinnitus. When asked by The Independent about the Hum in 1994, Jonathan Hazell, head of research at the U.K.’s Royal National Institute for Deaf People, responded, “Rubbish. Everybody who has tinnitus complains at first of environmental noise. ‘Hummers’ are a group of people who cannot accept that they have tinnitus.”

