New owner of iMac 24" 2.8 since last March. Just recently I have noticed that when I take off for a few days, I shutdown the iMac and when I return home a few days later and hit the power button the iMac is already on in sleep mode. The only change I have made recently was to add Time Machine on a Guardian Maximus 1TB raid drive, but I usually power off that drive when I leave. I've checked and searched here and in the Apple discussions with no luck. Does anyone have any idea what might be happening? Thanks in advance for any help.