My friend borrowed his 360 to me while he was out of town and I was surprised how much noise the power supply was making. I shut down the console and left the room and soon started wondering if I still didnt turn it off cos of the noise coming from the living room, it was the power supply
But it wasnt behind the TV set etc at that time, cos I only had it for such a short time that the power supply was basically in front of the TV so it was more audible than if it was in a more usual place.
Can't really answer your question, though..