I've got 2 27" iMacs at home, any both have worked very nicely since I got them (even though they have the slight yellow tinge, but it's so faint I've decided to live with it). I got them in November, and they are well used since both are used for working from home at least 8h / day. Yesterday I noticed one of them emitting a humming noise. It sounds like some kind of resonance sound from the harddrive or similar. It fades from silent to a noticeable humming and back again with an interval of about 5 seconds. I've heard similar sounds before when harddrives or CD players have not been tightly secured and starts resonating inside the chassis - that said, I'm not certain that is the problem, it's just an educated guess. The question is - what can I do about this? Is this something apple would consider a warranty issue? Do i void my warranty if I open it up and look for any loose screws? Or is this a sign that the harddrive is about to fail?