i have a mid-2007 silver 20" imac. i just noticed today that when i select sleep mode, the screen dims by about 30% for about a second or two, just before the monitor goes black for sleep mode. if it did this from day one, i wouldn't think twice about it, but this is something new. think there's any reason for alarm? monitor, and system as a whole are performing just fine otherwise. just thought i'd check w/you guys.