Everything around us makes noise if you stop to listen, it's sometimes quite surprising.
LCDs have a much more quiet whine compared to CRTs, probably from the backlight. (the inverter?)
CPUs in computers (esp laptops) sometimes whine. Usually completely drowned out by fan noise or harddrive noise. I have a fan-less and harddrive-less old laptop, a 386SX. The CPU makes a faint whine, I need to put the ear against the case to hear it. Changes in frequency as I change the CPU frequency.
My nokia cellphone charger whines, quite loudly even. Not surprising, switching powersupply? I can hear it from across the room easily. And the phones themselves are noisy, they can't quite shield their own speakers from the transmitting power they put out, so if you have a keen ear and if you're in a quiet place you'll hear a faint buzz and tapping from the speaker right before the call or message comes in..
Probably one of the strangest thing I've heard a noise from, was my Casio 9950G calculator. It doesn't have backlight and thus no inverter to suspect, but there's still something that can be heard coming from behind the display part of it. I can only hear it if I'm somewhere exceptionally quiet and with the thing close to my ear.
Another oddity was when I was wearing IEMs with the cord dangling and not attached to anything, in this room that is otherwise a bit strange. For example, some LED based light fixture glows faintly even when switched off, and glows stronger if lights in nearby room are switched on. Anyway, I was starting to hear the "usual" electric hum, and I've found that when I get that hum from the DVD player, what removes it is me touching the earth with my body, and comes back immediately if I let go. I usually have a wire going to my wrist just to get rid of that buzz. What was different this time was of course that the headphone cord wasn't connected to anything, I picked it up and touched it, there was a loud click/pop sound, and the buzz went away... Buildup of static electricity? Lots of electric current going through cables in the walls, creating a strong magnetic field that charges the LED fixtures and the speaker cables through magnetic induction? Who knows...
