All, I just bought a 15" iMac from someone, and set it up last night. I switched from a homemade PC that was very loud (fan noise) and was very excited about the silent iMac (in comparison). So as soon as I powered it on last night, I hear this irritating high-pitch whine (suppose it is the fan) that the iMac emits. It isn't the Hard Drive issue discussed here, rather a continious whine. Wow, it is annoying. Is there anything I can do? The seller transferred his Applecare to me (2.5 years left) but I have a feeling they will tell me it's normal operation. It is very annoying, to the point of giving me a headache. I think the base needs to be dusted  the actual inside of the base...was thinking about using compressed air...blowing it into the cd drive, and through the top holes)....oh yeah, any advice on how to safely do this?