Ever since I've had the iMac (3.2/Fusion/680MX), I noticed there is occasionally a loud crack/pop sound coming from behind the computer. First I thought it was from the walls, but then I noticed that it would sometime occur right after shutting down the computer. It happens very seldom, but at least 2-3 times a day. I can hear the sound in Bootcamp Windows, OSX, in sleep mode and like I said, sometimes right after shutting off. And it doesn't seem to be the exact same sound all the time. I already contacted Apple Tech Support, and the guy helping me will get back to me on the issue, but I'm really on the fence about initiating an exchange, since the return period will end January 7. Does anybody have similar experiences with their iMac, and what do you guys think about getting it exchanged? I would really love to keep this one, as it works flawless otherwise, but the sounds don't "sound" good and I don't want something to break after I can't get the exchange anymore.