Some say it's like a diesel engine idling. Others describe it as a deep drone or fluorescent light-like buzz. And a great many people don't hear anything at all.
Complaints about the "Kokomo Hum" began in 1999, when a handful of local residents began to report a constant low-pitched rumbling noise. They say they developed a range of mysterious health problems soon after, including dizziness, diarrhea, extreme fatigue, joint and muscle pain, nosebleeds, and excruciating, unending headaches.
"I think we all know something was starting to go drastically wrong about two years ago," says LaQuita Zimmerman, a 55-year-old grandmother who has lived in Kokomo her entire life. "It went from a headache to a never-ending headache," she says. When she leaves Kokomo to visit relatives, the suffering abates, she says.
"It's been over two years now," says Maria McDaniels, who lives several miles away from Zimmerman. "We just noticed a low hum — a drone in the background. It seemed to increase in intensity in the wee hours of the night."
McDaniels says she, her two sons and her husband began to experience regular headaches, sleep problems, and diarrhea around the same time. She admits she doesn't know for certain how the sound she hears relates to the symptoms, but she wants the hum investigated.
Zimmerman and McDaniels are not alone; Sen. Richard Lugar's office says it has received more than 80 letters complaining about the sound.
But most people in this central Indiana town of 45,000 don't hear anything at all.
Hum Complaints Met With Skepticism
Many Kokomo residents have been skeptical about reports of mysterious illnesses caused by a mysterious vibration, and local officials have done little to investigate.
"I know it does sound pretty bizarre," Zimmerman says. "It did to me before I was affected."
Attention to the problem began to increase last summer, however, when the Kokomo Tribune began an extensive investigation of the reports of the hum.
The paper talked to 40 residents who reported hearing the noise, and found that nearly all had visited a doctor more than once about related health problems, and at least 15 had undergone a series of neurological tests. Doctors typically attributed the problems to stress or aging, the Tribune found.
In an editorial last Sunday, the Tribune called for local officials to lead an investigation into the hum reports.
"The Kokomo Tribune editorial board wonders if city and state officials hope this issue won't just go away on its own," the paper said.
Hums Reported from New Mexico to Scotland
The Kokomo Hum is far from the first such complaint about strange low-frequency noise and related health problems. The so-called "Taos Hum" in northern New Mexico drew international attention in the early 1990s, as residents there complained of a persistent deep droning noise and accompanying headaches and illnesses.
Extensive investigations there failed to measure any low-frequency vibration that experts believed could cause either the noise or the infirmities reported by those who heard it. Even people who believe the Taos Hum is real admit that it has attracted a large number of outlandish theories and conspiracy buffs, which has hurt their credibility.
People in Taos continued to complain about the hum — some still do so today — but attention died down and many of those who reported serious problems moved away. A California rock band named itself "The Taos Hum," lending further infamy to the phenomenon.
Nevertheless, people in dozens — perhaps hundreds — of communities around the world have claimed they have been sickened by low-frequency noises. There is the "Larg Hum," in Scotland, the "Bristol Hum," in England, and others in Japan, Scandinavia and elsewhere. Some have been supported by scientific data; others have not.
The existence of low-frequency noises that cause nuisances is hardly controversial. Such sounds can be generated by turbines, industrial fans, compressors and other machinery.
The vibrations can travel a half-mile or more through the ground, causing dishes to rattle and a small subsection of the population to hear an annoying low drone. Adding insulation or adjusting equipment can often alleviate the problem.
Vibration Detected, But More Tests Needed
In Kokomo, reputable experts say they have detected a low-frequency noise of some kind.
In 2000, one hum-afflicted Kokomo resident hired an acoustic engineer to test for low-frequency noise.
The engineer, Angelo Campanella, who runs his own acoustic consultancy firm and holds a doctorate in physics and electrical engineering, found a low-frequency noise in the woman's home, but at a relatively low level.
"The level that is there is right at the threshold of perception, around 60 decibels," Campanella says.
The vibration Campanella detected would be considered a borderline problem according to some scales, and on other scales would be below problematic levels, says another acoustic engineer, Paul Schomer, who reviewed the data.
Both men stress that more testing is needed before drawing any conclusions about the hum. "We don't have really definitive data," says Schomer. "We need to have measurements at a bunch of these houses over a period of time."
Without speculating on the hum's possible effects on Kokomo residents, Schomer notes that scientists have associated a range of symptoms, such as general fatigue and malaise, with low-frequency noises.
Caution Against Blaming Hums for Every Problem
Other acoustics experts caution against associating a range of serious health problems to a low-frequency noise, however.
"They may be hitting on something that's a real phenomenon, but it could be their imagination," says Bennett Brooks, an engineer and investigator who heads the American Acoustical Society's Technical Committee on Noise. "The levels [of low-frequency noise] that will rattle dishes on a wall … haven't been shown to cause health problems, other than perhaps people waking up at night worrying."
He, too, is supportive of more testing for the Kokomo Hum. It generally is not difficult to measure low-frequency noise and to determine its source or sources. But in Kokomo, there has been little investigation beyond Campanella's one-time measurements.
People complaining about the hum have approached myriad local, state, and federal agencies, but none has agreed to investigate.
"We'd like to find the cause and correct the problem," says Scott Winger, a postal employee who hears the hum and believes he, his wife and children have suffered a range of health problems because of it. "It's not something that we just thought up."