Pretty much since day 1 I've been able to hear a whine from TVs and CRT monitors. This has diminished with age, but I can still hear it. I can tell when TVs are on or off with my eyes closed. I can tell if a TV is on but the screen is black (like it's set on video 1 but there's no input source). Very convenient.
The sound is very high pitched, sort of like this: