2011 27" 3.1ghz core i5 First off, when it does power down to go to sleep (screen starts to dim) you can hear the HDD spin (maybe preparing to sleep as well?). Never had this problem with my *silent* 2007 imac. Secondly, it won't stay asleep. I have not timed the intervals as of yet, but I would say it powers itself on out of sleep every half hour or so? I started to notice when I would wake up in the morning or come home from work and it would be on. Lately, I have had some time around the house and actually witness it coming on. When it does, it makes 3 loud click noises (again, sounds very much like the HDD) at about 3 seconds in between them. Then it wakes and you hear one more similar click. I have no running processes other than the stock ones. I have no running apps. I have also checked and unchecked stuff like "wake on network access", etc, with no luck. And even if it was a network problem, it still doesn't explain the HDD noise. I have also looked at the SMART status and it is verified. I checked it in disc utility as well and it all checks out. I have not ran an Onyx system scan yet, but I will probably do that next. Any other ideas?