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모델 A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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iMac has a buzzing noise on the top back left corner

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?

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Its the power supply for sure I lived in us never had this problem moved to a third world place with bad grounding and i find this post and similar that suspect the electric, YW

Power line noise can create issues! It can be local to you like a florescent light ballast or a noisy motor.

In most cases a good filtering UPS will solve the problem. These tend to be more expensive units! A cheap unit may not have the needed smoothing & filtering circuitry.

Have your electrician check your buildings ground as well as the wiring. Do you have the needed amperage 20 Amp for 120 Volts? Does the outlet have a good ground (three prong)?

You may want to speak with your power provider to see if you can have them put a power meter on your line to test it. Both low and high voltage conditions can effect the efficiently of your computer power supply and stress the UPS.

Dan is right about power line noise, however I don't think an iMac is earthed, rather double-insulated. So an electrician or power supplier cannot help. The power company can help when your voltage is too high. Mine was, and they reduced it.

To check your house voltage, ask a friend who has a true AC RMS voltmeter. Not usually in an electrician's tool kit, though it is worth asking them.

Voltage changes with time of day, falling to lowest at meal times, so measure the voltage during off peak times. Some UPS have a AC voltmeter built in, so you could get a UPS first and look at the voltage yourself.

The voltage in Australia is 230 volts, though my house gets 243 volts nearly all the time.

All my Macs run well on that, but perhaps that's the reason I got noise in my iMac.

Avoid most electrical noise filters sold with entertainment electronics. Most only filter or bypass huge lightning strikes.

A UPS with good filtering also saves you from loss of data or even computer damage in a power outage.


It uses ground (earthed) by using a three prog plug. Common and Ground are tied together at the fuse panel (hopefully the buildings ground is good).

So what is the function of ground for an iMac or any computer?

Grounds primary use here is to dampen noise (internally) as its path is not intended to support the power connection, think Faraday Cage. External noise is filtered by the power supply. But! Its not intended to filter away loud noise sources. This is where a good surge protector as well as UPS's can.

The type of UPS is important! As not all of them offer fill-in or clean the lines cycle frequency to fix bad power line service (high or low voltage or frequency). As an example I use APC Back-UPS Pro 1500 here in the states.

Ground it's also used as a safety path when the equipment fails or is mis-wired.

Some devices like a hair dryer are double insulated to prevent the risk of electrocution when used in a bathroom where metal fixtures are physical ground either through the piping and/or water. If that where the case the case would be plastic like the older polycarbonate cases in the old MacBooks. The current models (both desktops & laptops) are all metal cased so they can't be double insulated.

Mine is a late 2009 27 inch. It has only recently started "fizzing", with the noise predominant along the top (and, the left top is slightly warmer than the right side). It's been switched on for about 3 months (since last shut down), going into sleep mode when not in active use. I accept that it's probably a long-term fault in the making, with also probably a Send-Away-To-Be-Fixed solution. But, in the meantime, I shut down, then unplugged the power. Then, held in the ON/OFF switch for about 20 seconds, and let the machine sit for about half a day, properly to cool down and allow any static to dissipate. Now, after switch on - nil noise/fizzing. However, will this work in the long term?

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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.

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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.

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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.

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Hi Dimitris,

Can I ask you if using UPS on your iMac is still solving the buzzing problem? I'm also located in Athens and facing the same problem with my iMac. The whistling noise in the top back of my iMac is intermittently present when the iMac heats up. I'm considering applying your solution since I have to work on my Mac and cannot miss it for a week or more for diagnostics at Apple service. I read somewhere that this problem happens only with 220V and not 110V power supply.

Thanks for you answer!

Yesterday I bought UPS(Eaton ENV-600H) including AVR(Automatic Voltage Regulator) for my iMac 27" 2009 mid.

After that installed, buzzing or humming did NOT stop immediately, but I can feel it has now different noise.. more moderate one.

I just want to tell you that dimitrisdovinos's lucky case may not for all.

Hi Jin Hwa Kim,

Thanks for your update. From my last post the noise stopped spontaneously. I cannot explain it, but time ago I found a post in a blog describing the same phenomena. The post was describing how after cca two months buzzing stops by itself. And indeed for me it stopped +- in the same period. I just hope it is a permanent change. I wish the same happened to your machine. Kind regards, iGor

Hi guys

update on my side. I had the same problem and I was going crazy about it... I had replaced the PSU to solve a problem related to the iMac not starting... I thought it was the PSU (it would actually "try" to start for a few secs and then would power down... and loop again) - the problem was actually a faulty memory!

the noise was driving me crazy (due to the pitch and because I was used to a silent iMac...) and I thought it was the fans... e.g. that something related to the brushing...

When I saw this post I decided to put back the *Original* PSU... and miracle... the noise went away

It was definitely an electrical noise and definitely coming from the PSU area --- so replacing the PSU (with the original one...) solved it


Hi, I'm back.

UPS doesn't make better even after few weeks. So I backed up all data and took it to the Apple service center. Apple guy said he had doubt on Hard-disk fan, but I insisted that it must be PSU coil something problem.

After few days he called me and he said PSU is the root of weird noise, Replacement will cost about $140 due to the expired warranty. But, luckily, LCD panel will be replaced for FREE because of its own defect (He found the notorious stain mark on the display I couldn't even notice). New LCD panel is worth $900.

Now my iMac is dead silence. The most loud noise is the little static sound when sometimes reading hard disk. And my $80 UPS (perhaps its AVR functionality?) may prevent another PSU noise I guess, I hope.

p.s. iMac 27" is very heavy. Two men or using car. Awful.

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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!

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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.

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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.

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If the iMac gets seriously hot along the top, your components are extremely stressed. See my earlier comments about cleaning and desktop fan.

Since I started running a desktop fan aimed at the vent, the arcing noise has gone.

Some say a nearby fluorescent lamp caused their problem. That means Apple overlooked a few simple extra components in the power supply to filter noise out of the AC line.

I encountered a different problem a few days ago on my MacBook Pro. It suddenly got hot and the fans were going full speed, even though I had only used the Mac for a short time.

Out of many suggested solutions, I liked this one, as it did not involve loss of data ...

I opened the Activity Monitor and one open page in Safari was drawing more than 100 percent of the CPU resources. Closed that single window from a highly respected newspaper and the Mac has run cool since.

How does that relate to this thread? A stressed power supply can get noisy.

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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.

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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...

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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

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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.

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