After an hour of searching google I have found many issues like mine however no solution in sight. The first day was fine and now all of a sudden it's extremely loud and is blowing air like crazy out the top back vent. I changed me energy saver performance processor thing to "highest" like recommeneded and installed 10.3.8 but I am still having this problem. I can not return it at this point because of all the data I have on it (I just bought it Saturday) and I dont want to have to request any hardware. Isn't there some way to fix this? How do I slow the fans down? They are running crazy fast and it's annoying to use this computer now! When I put it to sleep its fine and the fans shut down to a perfect barable sound (wish it could be like that when not asleep). I guess the iMac isn't all what I thought it was if this problem cant be fixed. I'm a new switcher and then this happens.