My fan was out-of-control loud for a long time in my G5 iMac, 17". A few weeks ago, I also started developing a secondary problem with the Sleep command, in that when computer went to sleep, it actually was shutting off. Still, everything else functioned normally but right around the same time, there was a very loud spinning sound in the back of the computer. I'm not sure if it was the fan or the hard drive. Last week, it was spinning extra loud until it suddenly stopped, accompanied by the sound of something rattling in the back. The genius bar told me the fans don't break and they were going to do a 48 hr "reconfiguration". I have no idea what this is other than a systems asessment alond with temperture monitoring. Does anyone have any suggestions for me? Does the Genius Bar know what they're doing? I'm worried they never figured out the source of the noise and are now just running tests to make me feel better!