All the time, Drives me nut because not everyone hears it. For example. I was in a room where the tv was on, but the channel was black, I asked the teacher if they where going to turn off the tv. They said "It is off", So I went over, hit the off switch, and watched the tube cool down. Needless to say they ask "How did you know it was on?" And I said I could hear it. It really sucks sometimes because people think your crazy, But I know, I KNOW!!!.
Oh and btw, to the post about knowing when people are close, I can tell the same thing, I dont know what it is but I usually know when someone is closing in on me, Even with my eyes shut.