there is a sound coming from the inside of my PC, it is a low, but very audible sound that i can hear over my 6 120mm fans from 4 feet away.

i've stopped all the fans in my computer and i still hear it, what could it be?

my mb is new and i've only used it for 1 month. i've stuck my entire head into the computer already as close as i can and i still can't determine the sound. if it is a capacitor squealing, how can i tell?

the sound comes only when i'm within windows though, i dont hear it when i'm in the bios, not in the booting process of loading windows. i hear it at idle..

what can be causing this?