More 27" iMac Problems..ugh...

When I first got my iMac I had to return it three times, first two due to screen flicker and third arriving with a dead processor. But the latest one I have had seems to have been working good until last night. When I shut it off, there remained like an electronic buzzing noise seemingly coming from the top left back side. So I waited and it did not go away so I pulled the plug and it stopped. I put the plug back in and it was there again so I decided to unplug it and just wait till the morning and when I plugged it in(without needing to turn it on) the sound was back. Anybody experiencing this or know a fix?

The air vents are in the top of the iMac..and any dust that might settle in through the holes might resonate..having the power cable plugged in means that the various capacitors on the system are going to get charged and they might be causing the surrounding dust to make that noise..

I would try to see if you just blow in the top to see if that affects/changes the noise in any way..

I've had my 27" iMac since Saturday and I let it just sleep after some time and overnight and haven't heard any noises like this..

Regards

You're probably hearing fan noise - most likely vibration from the fan or housing around it. Buzzing can sometimes be caused by the LCD backlight, however, since your 27" model uses an LED backlighted screen, that is unlikely. Power supplies can sometime make a buzzing or humming sound, but that is usually associated with switching type supplies which your iMac doesn't use.

Regards.