My work PC is extremely loud. But sometimes if you hit it on the top of the case with your fist, it gets quieter...
It makes it hard if I'm trying to play a game at work because then it gets REALLY loud and people in the office start looking towards my desk and then I have to quit the game so as not to get caught
But my iBook and iMac don't make any noise at all

its really strange to go from one extreme to the other.