Editor's Note: This story was updated on Thursday, July 9 at 11 a.m. ET. There's an electrical hum in most animals, including ourselves. No one knows where it came from or why exactly it exists. Now, ...

Ever notice a light, a stereo, or other electrical appliance monotonously humming at you? Of course you have. We’ll tell you why it happens. Hmmmmmmmmmmmmmmm. There are all kinds of reasons for your ...