I've noticed that my 20 inch iMac Alu glows at the bottom and the top of the screen when displaying a black/very dark picture (for example when looking at the "flurry" screen saver). It's not so bad, and it is only visible when the screen is showing a very dark one-coloured-image. I'm curious to know if this is a common issue, and if anyone else has the same phenomen on their iMacs. Another thing I have noticed is that my machine is giving a pulsing low-frequency sound when connected to an external harddrive. It's quite irritating, but I read about another guy with the same issue, maybe all machines are like that?