Answer to "iMac has a buzzing noise on the top back left corner"I have this same problem. I also found that video on YouTube and yes, the sound increases as brightness does, as well as when scrolling a web page, etc. I work on a mac all day and for the price, I expect more... I actually took it in to an Apple store for repair telling them it could be the Power Supply. The Genius guy heard the sound and said they'd have it back to me in 7 days. 9 days later I called and they told me they couldn't find anything wrong, thus no need for repair. This doesn't sit well with me since it's a pain to lug around a 27" iMac. So in the end, problem NOT fixed.