I just purchased a new iMac 24" 2.8GHZ in July as my first mac and I believe I am having issues with my hard drive. On and off, I can hear it buzzing very loud for long periods of time. I can hear the noise "power down" when I put the imac to sleep or shut it off. It does not sound like fans pushing air and my fans are running at normal speeds. I called Applecare and they determined it was not the fans and it could be the hard drive making a buzzing noise as its running at 5400rpms. The constant buzzing noise is coming from the upper-middle area of the back casing. My question is: Typically, what does Apple do when you need your hard drive replaced in an imac? How long does it take or will they provide me with a replacement machine? I have applecare for 3 years. I've searched the forums and noticed how tedious it is to change the hard drive and my issue is that I need this machine for work purposes so any down time is a big hit to my business. Any help is appreciated. Thanks.