Are you one of the sensitive? Scientist Geoff Leventhall estimates that nearly 2.5 percent of the population may have a lower than average frequency threshold, meaning they can hear — and so they are bothered by — low sounds that most other people cannot even begin to perceive. Normally this sensitivity causes only an occasional source of discomfort, such as when a big diesel truck passes on the highway, but for those living near one of the planet’s rare "hum" spots, all pleasure in life may slowly erode until existence is nothing more than a painful chore.

What does the hum sound like? Universally, people describe the noise in a variety of ways, including as a steady droning, a throb, a rumble, a pulsing, a thunder-like sound, and a low speed diesel engine noise. While these reports are diverse, it is these same few descriptions that sensitive people use time and again, no matter where on earth they live, when trying to characterize the sounds they hear.

Hum spots, most of which scientists cannot account for in any plausible way, are found on most continents. Publicized locations include the Taos Hum in New Mexico, the Kokomo Hum in Indiana, the Bristol Hum in England, Largs Hum in Scotland, Copenhagen Hum in Denmark, and the Vancouver Hum in Canada. Below are some YouTube recordings at some of these locations. It seems impossible these videos have not been doctored in some way to enable most of us — and not only the rare few — to hear the sounds.

The Vancouver Hum

The Copenhagen Hum

The Taos Hum

The Bristol Hum

The Auckland Hum

Cause

In the case of the Kokomo Hum, scientists immediately suspected and later traced the cause of the noise to industrial equipment, in this case, machinery housed in two nearby factories, one of which was a Daimler Chrysler plant. In other cases, scientists speculate the sound to arise from high-pressure gas lines, electrical power lines, or wireless devices, though so far they have not yet proven their theories. Some believe a hum may result from low-frequency electromagnetic radiation, air turbulence, thunder, or microseisms — faint earth tremors generated by the action of ocean waves. Conspiracy theorists are more likely to suggest military experiments and submarine communications.

Effects

While tourists may find a hum spot the perfect occasion for comedy or contemplation of the universe, those who live nearby often suffer terribly. 'Round the world, sensitive souls complain of pressure in the head, body vibrations, loss of both concentration and sleep, and even nausea caused by the hum they hear.

The most frequently reported consequence of low-frequency noise is annoyance, according to the authors of a general report on the subject. While this may seem trivial, such a reaction often accelerates stress, and, coupled with other factors, this may lead to a general deterioration of health and well-being. Men show more reaction to low frequency noises than women, while laboratory studies show such sounds may induce changes in blood pressure and heart rate. Interestingly, people with a family history of hypertension show more pronounced cardiac reactions, while only those who are able to hear low-frequency noise suffer — people who cannot hear these sounds suffer no changes or ill effects when exposed to them.

Naturally, mental health may be influenced by a low frequency hum. “Long-term studies suggest a complex relationship between mental health effects such as depression, noise sensitivity, and noise exposure,” say Britta Berglund and Peter Hasmen in their general report. Continuous low frequency noise will not create a mental health problem where none previously exists; however, a hum certainly can exacerbate any pre-existing issues.

Meanwhile the scientists search to explain these mysterious and rare earth events. Heard by only the rare few, a hum may just be another reminder of all we do not know or understand about life in this universe.