About a week ago I installed some updates; nothing major to the OS. Recently I have noticed that when iTunes changes songs or movies the display flickers a light gray. Any idea of what's happening? I've had the iMac for about a year. 1 year service actually runs out on November 10, 2012. System: 27" iMac 2011 version OSx 10.7.5 Update: It's not the entire display, only the background and dock.