Some people occasionally hear a low buzzing or humming sound that doesn't have a clear source. An estimated 2–4% of the world's population hear this. Scientists have been trying to figure out for ...

I have noticed ever since I have had my 1ghz alpb, sometimes when it is plugged into the wall, I can hear a low level electrical hum coming from the powerbook. When I unplug the ac, it goes away, ...