Original post by: Daniel Hebert ,
My 27 inch 2011 iMac started to buzz like this after 5 years. It was silent for the first 5 years. Then the buzz started. I changed the PSU. The buzz came back after 2 days. Then, I changed the LED backlight board and the buzz came back after an hour... There is nothing left to change! WTF. If someone finds a fix, please let us know.