The Hum, a low frequency, steady droning and rumbling sound has been reported in locations across the world, from Taos, N.M. and Vancouver, Canada, to Bristol, England and Sydney, Australia. The mysterious phenomenon is now the subject of investigations.
Researchers have for decades been investigating what causes the Hum. Why only a small proportion of a local population is disturbed by the sound remains a mystery. According to The Huffington Post, a 2003 study by a UK acoustical expert Geoff Leventhall, found that only about 2 percent of residents of the localities studied reported the sound and that most were women aged between 55 and 70.
Reports say the first documented cases of people reporting the Hum was in the 1950s. Most sufferers were people who had previously never heard unusual sounds but suddenly found that they were being constantly tormented by a low frequency rumbling some have compared to a diesel engine idling nearby.
Most "hearers" or "hummers," as sufferers are called, only hear the noise indoors and it tends to get louder in the night. Most cases are reported in rural and suburban regions, a fact that has prompted obvious suggestions that the Hum could be the steady beat of the crowded city environment.
The BBC reports the case of Katie Jacques, a 69-year-old woman, who lives in the suburb of Leeds. Although most people in her neighborhood do not hear the sound, she describes a droning sound she finds disturbing and distracting. She said she had ceased enjoying peace since she began hearing the Hum two years ago and that it disturbs her sleep.
She told the BBC: "It's a kind of torture; sometimes, you just want to scream. It has a rhythm to it - it goes up and down. It sounds almost like a diesel car idling in the distance and you want to go and ask somebody to switch the engine off - and you can't."
She added: "It's worst at night. It's hard to get off to sleep because I hear this throbbing sound in the background and you know what it's like when you can't get to sleep and you're tossing and turning and you get more and more agitated about it."
She has tried eliminating the sound by turning off all electrical appliances in her home and using ear plugs, but she continues to hear the noise. After efforts to track its source in her immediate environment failed she became convinced it was from the airport nearby. But airport authorities said no engines were left running overnight at the airport.
Medical tests ruled out tinnitus, a ringing noise that some medical patients suffer.
Like Katie, most "hearers" tend to be dismissed by their relatives and friends who assume the noise is in the sufferer's head. However, investigations have shown that most "hearers" have normal hearing, although some may complain of headaches, nausea, dizziness, nosebleeds and insomnia. A case of suicide in the UK has been linked to the Hum, according to the BBC.
Katie responds to the view that the Hum is in "the head," saying in distress: "People assume you must be hearing things, but I'm not crackers. I don't know how I can get this over to people, but this is not in my head. It's just as though there's something in your house and you want to switch if off and you can't. It's there all the time."
One of the areas where the Hum was first reported was Bristol, England, in the 1970s, where it was famously dubbed the "Bristol Hum." A newspaper survey found that 800 people reported hearing the steady sound believed at the time to be the noise of traffic and local factories whose plants worked 24-hour shifts.
Cases were also reported in Cheshire, Cornwall, Gloucestershire, London, Shropshire, Suffolk and Wiltshire.
The second major report came from Taos, N.M. ,in 1991, where some residents reported a low-level, low frequency noise which experts from the Los Alamos National Laboratory, the University of New Mexico and Sandia National Laboratories investigated without a definite conclusion.
A third notable case was in Bondi, Sydney, Australia. Many residents reported hearing a constant buzzing noise for years, the Daily Telegraph reports. The source of the noise has been under investigation for years.
A resident reported: "It sends people around here crazy — all you can do is put music on to block it out. Some people leave fans on."
Experts suggested a local sewage plant and traffic as possible sources, but both have been ruled out.
Another resident of the area, Robinson, said: "I didn't hear it, but since they've pointed it out to me, I try not to hear it because it's incredibly annoying." She added: "Some people say they hear it all the time and others haven't heard it. It's at that frequency level, not everybody hears it. I know it sends people around here crazy, all you can do is put music on to block it out. Some people leave fans on."
In 2003, researchers sponsored by the Indiana City's municipal government in the US investigated the so-called Kokomo Hum and traced it to two factories, including a Daimler Chrysler plant. But strangely, after measures were implemented to control the noise several residents continued to complain of the Hum.
What causes the Hum?
The first suspicion that an investigator entertains is that the Hum is in the head of "hearers." A possible explanation based on the global spread is that it could be a form of tinnitus associated with a particular disorder. However, repeated tests have failed to show that the Hum is a form of tinnitus.
According to the Low Frequency Noise Sufferers' Association, more cases are being reported with most sufferers being women over 50 years of age.
What is notable with regard to any speculation about the source or cause of the noise is that most researchers believe it is real and not in the heads of "hearers." They also believe it is not some form of mass hysteria, hypochondria or the product of fantasies about alien spaceships or space visitors beaming signals.
Investigators have suggested a host of possible sources: gas pipes, central heating systems, power lines, mobile phone masts, wind farms and nuclear wastes, The Huffington Post reports.
Some investigators have suggested it could be the result of low-frequency electromagnetic radiation audible only to some people.
The inability of experts to agree on the likely source of the noise has sparked the usual rumors and conspiracy theories ranging from government cover-up to aliens attempting to contact humans.
The BBC reports that an audiology expert at the Addenbroooke Hospital in Cambridge, Dr David Baguley, dismissed the theories. He said: "People do come up with some strongly constructed, sometimes strange theories."
He said that in approximately one-third of cases the Hum has been traced to a mechanical or electrical source. The BBC reports he said: "It may be a fridge or an industrial fan or a piece of heavy machinery at a nearby factory that is causing the disturbance and can be switched off."
In most cases, however, investigators have not been able to track the noise to an external source.
Baguley has a theory of his own to explain the phenomenon. He suggested that "hearers" are individuals who have become "over-sensitive" to certain frequencies in their environment. He explained that sufferers have somehow become fixated on a background noise or sound leading to their system being over-sensitive to it.
According to the expert, everyone has an internal volume control that helps control sensitivity to different sounds under different circumstances. He said: "If you're sitting by a table waiting for exam results and the phone rings you jump out of your skin. Waiting for a teenager to come home from a party - the key in the door sounds really loud. Your internal gain is sensitized."
He said that after the initial signal that triggers sensitivity, "It becomes a vicious cycle. The more people focus on the noise, the more anxious and fearful they get, the more the body responds by amplifying the sound, and that causes even more upset and distress."
Measures adopted to combat the problem and alleviate the suffering of victims include use of white-noise machines. Other experts recommend cognitive-behavioral therapy.
Investigators are not sure how soon the mystery will be solved. Leventhall told the BBC: "It's been a mystery for 40 years, so it may well remain one for a lot longer."