Buzzing, noisy power supply in a 2011 27" iMac -- buy new, not eBay
20 - 30 minuten
My iMac was making a terrific electrical noise which would increase when the screen brightness was increased or heavy computation was underway. I diagnosed the problem through searches of forum posts and an assessment of the noise being correlated to energy usage and not just screen brightness. If it were solely screen brightness I might have been tempted to replace the LED driver board.
Easy repair overall. The new power supply has much larger heat sinks that the original which probably will keep it running smoothly for many years to come.
The iFixIt-sold power supply is probably superior to the original due to it having larger heat sinks...likely a fix in newer models of the iMac.
I initial purchased a replacement power supply on eBay. It was about $30 cheaper than iFixit. Needless to say, the replacement had the same issue as the original: an obnoxious buzzing noise which increased with power usage. The replacement was likely from a used machine even though the eBay post stated the device was new.
Fortunately, I was certain in my assessment of the cause, partially as the ebay-purchased power supply was quiet at first and only started buzzing after a couple of days of use. But mostly as the other potential candidate cause (the LED display driver board) should only be affected by brightness, not CPU intensive tasks.
Even though I received a full refund for the faulty power supply from the eBay retailer, the extra teardown and annoyance of a failed initial fix was very frustrating.
I don't recommend trying to get this power supply from a discount reseller or eBay... you might get lucky or you might just waste time and money. Even if the part really is "new" it might be of the older variety and suffer the same issue as the original.