I'm going on my second Imac, the first one I was happy with until the airport card issues (I would restart and receive No Airport Detected Message) My replacement Imac has a high-pitch whine coming from the upper top left of the screen. The sound gets louder I beleive when CPU utilization is higher, especially when running a game I have. I can change the pitch and intensity of the sound by playing with the brightness setting, getting it to go away almost completely although at that point the screen is too dim. I can't believe I may have to return another Imac. I read that this program called shades will make it go away but it hasn't helped me at all. Anybody else experiencing this and have any suggestions to get it fixed?