Chosen Solution
I have a mid 2011 27inch Imac 3.4 GHz , i7 ,8GB. Recently there has been a buzzing noise that comes out the top back left corner. when i increase the brightness of the screen the buzzing noise becomes louder when I decrease the brightness the noise stays the same. I have seen youtube videos of people recording the buzzing noise and some say it is a faulty power supply or the LED driver board. Has anyone heard about this? and if so where could the noise be coming from?
This seems to be a “known issue” as they say in the Mac World. Could be the LED Backlight Board or the PSU. Since there’s been quite a bit of chatter about this I would go to Apple Support and see if the machine in questoin is still under warranty, if not, there may have been a silent recall, extended warranty or coverage still in effect on your machine. If there doesn’t seem to be, I would contact Apple directly and rais a bit of fuss- as there’s quit a bit of this on the Discussion Board and other Mac Forums. If this Answer is helpful please remember to return and mark it Accepted.
You must have had a repair receipt with the description of the problem. I’d go back and up the chain to the manager, or contact apple support directly. They took the machine in, if there was nothing wrong why would they do that, and keep it 9 days? Something smells… don’t let it go out of warranty like this.
I had the same problem and after 1 to 2 months of buzzing I turned it off and it would not start again! I am fairly certain that this is related to the PSU and I have already ordered one (I am based in Greece and I do all my work on my iMac so I can’t afford to waste time with the fairly low quality Mac service available here). This may or may not be relevant: I have been using the iMac with a 2nd monitor attached. The GPU has been getting pretty hot and I assume that this has placed a strain on the PSU. Update: I decided to power the iMac with a UPS. For some bizarre reason the humming stopped immediately. It has been a month now with the UPS and the buzzing only happened once. I have ordered (and received) a new PSU from ifixit, which is sitting in my drawer for now.
I had the same buzzing noise issue with my mid-2011 27" iMac. Then one day I shut it down to move it and it was totally dead when I hit the power button. I replaced the PSU with a new one and the buzzing stopped – for about two weeks and then it started up again (with the new PSU unit in). It does the increase/decrease volume with brightness adjustment. I even tried lifting it off the desk to see if it was a vibration as some people had stated with no success. Seriously, this issue is all over the internet and there is no definitive answer/fix from Apple!
After that I replaced power supply unit at Apple service center the noise totally gone. By the way, old SATA HD’s makes some noise too.
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.
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.
I HAD the same problem. After some research I found the following solution that worked in my case. Quote: “I did a lot of searching around but ended up finding the solution by accident. The problem, it turns out, didn’t have anything to do with my screen. It was a fluorescent lamp plugged in to the same circuit as my computer. It was actually on the other side of the room but it creates interference in the AC power that conflicts with the power supply in the computer. Somewhat similar to what makes some car stereos buzz when driving.” Ergo: I changed all the fluorescent lamps in my room with LEDs » buzzy noise fixed. original solution see this link: https://discussions.apple.com/thread/343…
LEDs can be very noisy too and interfere with TV reception. There is no easy way to find out which LEDs are noisy, so just purchase one and try it out. If your iMac is getting very hot, the noise can be the power supply or other section getting very stressed. I run a desk fan on my iMac every warm day and the arcing noise disappeared. I don’t like to increase internal fan speeds, as it shortens the life of the tiny fans. Look up advice on how to clean an iMac too. Thats my next step, along with a tube from the desk fan to the vent. When trying to have an elegant look, Apple ensured overheating problems were common and made it near impossible to dismantle to clean and fix. I don’t care about the elegant slim look, I’d much prefer reliability and ease of service. I previously did quite a few things inside my Bondi Blue Mac - which still runs fine
There seems to be two faults discussed here - (1) noise and (2) Combined Noise and overheating. I have (2) noise/overheating version. A big concern, as it’s likely to be an overloaded power supply, that could fail. My Mac is connected to a second monitor, but that should not contribute to the problem, as it only uses signal, not power. Since aiming a desk fan at the iMac vent, with a cardboard funnel focussing the air at the vent, the noise and heat went away. I already had a UPS / line filter in place and that made no difference.
