Ive, never gotten a definative answer on what could be causing this noise im having from my iMac. Basically, about 4 years ago my family bought 3 imacs at the same time and mine just happened to be twice as loud as everyones. Now 4 years later (even tho i have switched to the dark side "pc") i keep the iMac and use it for video editing and multimedia production. Well when i press start it sounds like a Boing 747 starting up and you would not belive how bad it is (afraid its gonna get the neibors upset)...... Basically i have come to the conclusion that there is a balance problem with my hardrive? Whatever the case my iMac hasnt missed a beat and still runs strong.... I guess im gonna install some Dynamat sound absorbsion or something in it geeesssshhh!