Constant Hum Annoying People around the World

A constant, low-pitch noise, popularly known as "the hum" has led to disturbed sleep and irritation in many people around the world.

The phenomenon isn't entirely new. Reports of people hearing a low-pitch hum have been documented since the 1950s. These sounds can be heard in different parts of the world- from Bristol in UK to Taos in New Mexico, reported Livescience.

The hum affects a small population of people between ages 50 and 70 years.  Explanations for the phenomenon range from tinnitus to colliding ocean waves and mechanical waves. Other theory is that the affected people hear Spontaneous otoacoustic emissions, which are sounds generated by their own bodies. However, none of the theories explain why the phenomenon affects only a certain population.

The hum is almost always reported by people living in the countryside and this is probably because of a lack of background noise (traffic, industry etc) in these regions. People who hear the noise describe it to be like that of a nearby idling engine.  

"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," Katie Jacques, retired head teacher and a hum sufferer told BBC in 2009.  "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."

Dr David Baguley from Cambridge Neuroscience had then said that the affected people might be overtly-sensitive to low pitch-noises that others can't hear.

Other possible reasons include presence of some industry that's causing the noise, high pressure gas lines and electrical lines, Livescience reported.