Just noticed this morning that when I put my Mac to sleep it still makes a very faint noise. A ticking sound that cycles at about 3 times a second. It is extremely quiet, but it does sound like it could be a fan, hard drive or possibly the power supply ticking away. I was just wondering if other iMac users could confirm this noise by sleeping their Macs and putting their ear to the top. If it's widespread, I won't worry. Remember, you need to be in a quiet room and listen very intently to the top. I've just turned my Mac back on and realised that it's not just when it's at sleep. It's also when the power at the wall-plug is just switched on. This surely means it's the power supply making a ticking noise. Starting to get a bit paranoid now. Could anyone test this out for me?