All over the world for decades now, people have reported a very strange "humming" noise that doesn't seem to have an identifiable origin. To some, it's a nuisance. To many others, it's unnerving and maddening. Even more interesting: most people can't hear it.
The humming appears all over the world. Most notably, Bristol in southern England and Toas, New Mexico play host to the strange humming sound. And strangely enough, only about 2% of the human population is able to hear it.
Often times, the hum is heard indoors and is clearer at night. The hum isn't common in urban areas, like crowded cities that have constant background noise. It tends to appear only in more rural, quieter areas. What could it be?
According to one study, the majority of people who can hear the sound are between 55 and 70. Some hear the humming all day, while for others, it's on and off. Some people have reported that it interferes with their ability to go about their daily business. It's been blamed for at least one suicide. Some of the more extreme cases cause nosebleeds, insomnia, dizziness, nausea, and headaches.
Some doctors believe that the hum is just tinnitus, a disorder that causes people to hear sounds that doesn't exist. But that likely isn't the case this time since the hum is only heard in a few specific places.
It could also be that the hum is what's called an otoacoustic emission, a sound generated by the ear itself. In either case, there's no explanation of the phenomenon that is satisfactory to the people who experience it.
What do you think it is?