I have my display/sleep settings set to 15 minutes of inactivity. I have noticed for awhile that when there is no music playing and my display is off, but the computer is running, only requiring me to login when I come back to my computer, that it makes a constant "booting" noise. For example, let's say I sit here for 15 minutes and my iMac goes into sleep mode. My settings are to put the disks to sleep when possible. No applications are running, (even though sometimes I may have a browser open, itunes, etc for when i log back in), and it is basically at rest. My computer will go on these spurts where every 30 seconds or so it will start making noise like I just pushed the power button in the back to turn the computer ON when it was OFF without making the Apple startup sound. It does this constantly. Sometimes I will press play on my Apple keyboard for music to play as I go to sleep, but when I pause/stop the music with my remote, it's almost pointless to go to bed knowing that the computer is still 'running' when it should just be sleeping/off (but not actually SHUT DOWN). Is this just me? Has anyone else experience this? I don't know of anyone close to me that owns an iMac of this model or has experienced this and I'm wondering if I need to take it in to have someone hear this.. My iMac is the Late 2011 model with top upgrades: 3.4GHz Quad i7, 256GB SSD + 1TB HDD, 2GB Radeon 6970, 8GB Ram. Thank you!