I have been battling with fan speed on my iMac recently. I installed iStat which shows normal temps, but the fan revs up to 4000rpm - for seemingly no reason at all. Sometimes its quiet for long periods. It sometimes helps for a while if I put the machine into Sleep mode, but then I hear the fan start to rev up again when I resume activity. I have spent hours with tech support, who then upgraded me to a higher level of tech support. But still the problem continues. I would like to ask members of the Noisy Fan Club 2 questions. 1- Have you recently upgraded from Leopard to Snow Leopard. Did the problem only start then? 2 - Have you tried booting up into Safe Mode and seeing if the fan speeds up while you work in Safe Mode? My fan only started this behavior after upgrading to SL, and I am now running in Safe Mode with my fan totally,blessedly silent at 1198 rpm. I would be interested if anyone is having similar issues? Has anyone found a clean install of SL helped? Or going back to Leopard maybe?