I've just got my 20" iMac 2.1 GHz. Very dissapointed to hear a quiet buzz from the lower left of the machine. It would seem to be the CPU fan - it changes in pitch when applications are working harder. I can hear it over quiet music and it is quite annoying. I plunged for this machine after reading so many positive testimonials. I thought I would only be hearing movement of air. I will ask Apple to replace it tomorrow but I don't want to hear that it is "within specifications". Are other owners hearing a buzz (like a quite mini motorbike) from the lower left hand side of the machine? I'd be grateful for your feedback.