ok, so i wanted to make a new thread about this topic because the last one was cluttered with confusion, so i am making this new one a bit more specific. ok. well my new late 2012 late 27' 1TB non-fusion iMac makes an electrical buzzing noise and NOT the fan and NOT the spinning hard drive (i know what a fan and hdd sounds like) when it is plugged in. it doesn't matter when it is On or Off, as long as it is plugged in. it also happens usually in the evening time, every day. only unplugging it, then noise will stop, of course. i have tried many things to try to get to the root of the problem. i have already tried: to no avail. - i have tried unplugging every thing plugged in one by one to see if something is interfering with my iMac cord. - have tried various outlets. - i have tried putting the iMac cord through a surge protector. - i have tried putting the iMac cord through a APC voltage Regulator. - my previous 2010 21.5 iMac never had this problem. - the noise is on the side where the power button is located, under the display by air fan vents. about 5 inches to the left of the apple decal. an electrical voltage type of noise. - i am already talking to apple care about this issue. HERE is a sample of what the noise sounds like: (sorry, there is a dog barking about halfway into the recording) https://soundcloud.com/pavl-1/2012-imac-electrical-noise any thoughts would be much appreciated. thanks.