Hopefully one of you guys can tell me what might be causing this. I've had 2 identical machines - 2010, 3.2 Ghz Quad. The first was refurbished, the current one, brand new (as of early Feb). Both machines have this identical, periodic noise. It's a short (1/2 second or so) 'whine' / 'spinning down' sound. I originally thought it was a drive going bad, but found that not to be the issue. My only other guess is that it might be a fan? At this point, troubleshooting has consisted of swapping drives and resetting the PRAM. Any help greatly appreciated!