A moon rises over Kokomo, Indiana. (Photo: David Lytle/CC BY 2.0)

In the industrial town of Kokomo—the 13th largest city in Indiana—the reports of the Hum began in 1999. It was a low, constant rumble that would slowly drive you crazy, and the only way to escape it was to leave town.

“I think we all know something was starting to go drastically wrong about two years ago,” a lifelong Kokomo resident told ABC News in 2002. “It went from a headache to a never-ending headache.”

Laugh if you want, but the Hum is more than a minor annoyance. In addition to headaches, Kokomo locals who had been exposed to the noise began to complain a host of other health problems that they believed were the result—problems like diarrhea and nosebleeds. The wrinkle was that only a small minority of people in the town of 45,000 have ever actually been able hear the Kokomo Hum at all.

It would be easy to write off these Hearers (as they’re sometimes called) as crackpots, but many scientists and doctors believe there’s at least something to their claims, and in 2003, the municipal government of Kokomo took the problem seriously enough to launch an investigation into what was causing the disturbing noise. The results showed the likely culprit to be a set of huge fans in a nearby DaimlerChrysler plant. But even with fans fixed, claims persist that the Hum is still humming.

Graffiti on a slide in Kokomo’s Highland Park, Indiana. (Photo: David Lytle/CC BY 2.0)

Kokomo isn’t unique in its strange predicament. Hums can be heard in several locations around the world—most famously in Bristol, England and in Taos, New Mexico. And while it’s hard to state the exact number of worldwide Hums, The World Hum Map and Database Project is dense with self-reported sites. In each place, Hearers, who tend to be between the ages 50 and 70, complain of eerily similar phenomena, as well as similar forms of distress that they believe is caused by the Hum. 

The effects of prolonged exposure can be dire. “It’s a form of torture,” a Leeds woman named Katie Jacques told the BBC, which goes on to report that The Hum has been the cause of at least one UK suicide. 

It’s hard to tell if the Hum is a single phenomenon, but most reports of Hums around the world share certain characteristics that make them distinct from other noise. Usually it’s a low, rumbling sound that can only be heard by a small group of people, and is more commonly heard indoors. In Kokomo, as in most cases, louder at night than it is during the day.

But no one can agree on where the sound is coming from, or even on whether it’s real. Among those who do believe, theories as to the origins of various hums vary, and include low-frequency electromagnetic radiation, electrical power lines, secret military experiments, and—in the case of a Hum in Sausalito—the mating call of the male toadfish.

But many of these theories have been debunked, and most of them are unable to explain why there are Hums happening all over the world. After all, there’s no toadfish in Indiana.