My 24 inch imac 2.93 ghz has just been delivered and there is a small problem. Since starting to use it, there is a faint rumble coming from the machine that can be heard when there are no other background noises. I checked istat and the fans seem to be running at their normal temperatures. I'm guessing it's either a noisy fan or maybe the harddrive. Any advice ? I guess i could live with it but i don't want to. Are imacs supposed to be nearly silent ? Thanks