I run my iMac an average of 12 to 14 hours a day 7 days a week. But when not in use I usually put it to sleep and I shut it off completely at nights. Its about two years old and recently I've notice a very light "click" sound. Not clicking, just a click... It happens at random. Sometimes I can go hours without hearing anything at all then out of the blue, just what sounds like a light click. Now I'll admit I could be over reacting as the sound is very low, what some might describe as almost inaudible. I've listend to the sounds people have posted on You Tube of iMac fans and Hard Drives going bad, the buzzing the screen makes etc... And this is nowhere near close to anything posted. So I was wondering, could it just be the heating and cooling of the plastic/metal, or is it just a random noise any computer would make and for whatever reason I'm just now noticing it? Thanks!