I have an iMac9,1 (24") with horrific hum (my hearing is particularly sensitive so it might not be that bad) -- the kind we get from the display brightness being lowered, as well as a constant high-pitched whine, both of which appear to be common given the number of topics on the subject. Are the power inverters in these things crapware or what? My woman's 20" iMac from 2006 has similar hummage; so far I've written this off as an iMac feature and am not convinced that if I were to Apple Care this thing that the replacement would not scream as well. How about anyone else? Have you had this inverter issue, had it taken care of and eliminated? Or is it just an iMac feature that I live with by drowning it out w/ loud music?