Hello everyone. I've read many of the posts about the various issues with the iMac 27'. I'm on my third one now, and this one has the screen noise issue some have mentioned, where two noises, a high pitched "dog whistle" sound and a clicking wheel sound, emanate from the top left corner when the brightness is lowered anywhere past the maximum setting. Some backlight bleed exists as well, but other than that the machine is perfect. The rep at the Apple Store, Japan (where I live), already offered to send me a replacement, but now I'm thinking that I may as well just stick with what I've got. Mine is a Week 14. My concern is not really the noise caused by the brightness settings but that this noise is, as some have suggested, connected to a power source problem or other problem that could worsen over time and cause something seriously bad to happen. Does anyone have any advice about this? Is the problem harmless and not worth going through the hassle of getting the whole unit replaced again, or should I be cautious about this and go for the replacement? Any suggestions would be greatly appreciated. Thanks!