I have a 27" iMac w/ i7 that has been driving me nuts lately.. When you turn down the brightness on the screen the unit begins to let off a high pitch whining noise. On full brightness it makes no noise at all but soon as a I lower the brightness one click the whining starts. I also noticed that when I turn down the brightness all the way to 0 that the noise completely stops. I have another (3)27" iMac's w/ i5 that don't seem to have these problems. I was wondering if this has happened to anyone else? I placed a call into a local authorized service center so I have already begun the process of hopefully getting this repaired.