iMac 27"medio 2011 strange buzzing sound

[keeper11]

Hi my iMac medio 2011 16gb ram 500gb ssd 2 gb grafic
with latest updates El capitan.
Last night i did an update itunes etc, under this i noticed
a strange buzzing sound from upper left hand vent,
it got louder if i increased brightness, but stoped if the
imac went to sleep.
I read quite a few have had this problem, someone said it
would go away if you unpluged the imac for some minutes
i did this and it is now ok.
Has anybody on the forum had this, and my question is will
it come back again?

 

[Raz0rEdge]

The iMac's venting system is designed to suck air from the bottom, channel them over all the components and then exit on the top. If you have any dust or anything there, you will get the humming noise, so try to see if you can blow some air around there and see if it clears things up..

 

[keeper11]

Hi Razoredge
No its a electical buzzing noise.
I have an app to adjust the fans
i adjusted from normal rpm 1100
to rpm 5500 acording to your theory
at rpm 5500 the noise would be a lot
higher but it is not stays the same.
I have seen posts about it being a
power supply fault?
But it did help removing power for 5
minutes turn on again and now no noise
i would like to know if people that have same
problem if it comes again.

 

[Raz0rEdge]

When dust settles on electrical components, it will resonate and buzz that way. People have found using an air compressor (one that DOES NOT shoot cold air) in through the vents dislodges whatever dust is in there and will make things better. You can also try a vacuum at the top of the iMac to see if the suction will have the same effect..

 

[keeper11]

No i still think its a power supply i have cleaned
blown out any dust there could be in there.
It seems to come after longer use 2-3 hours.

 

[chscag]

I've seen this complaint before by some iMac owners. One user stated he eliminated the sound by placing a rubber mat under the stand of his iMac. If it is the PS causing vibration after it warms up, you might try the rubber mat solution to see if it works for you. Otherwise, the only cure would be to replace the PS.

 

[tjuju]

I just fixed the buzzing sound so I would like to share.

My iMac is 27" mid 2011 version and it had that annoying buzzing sound for months. I tried all the suggestions like unplugging the power, vacuuming the dust, resetting the PRAM...etc, all didn't work. When I increased the brightness of the screen, the sound got louder. I believed it's related to the power supply so I finally did the last thing --- Changing the PS!

I followed every step from a video in youTube (search "replace iMac power supply, and it's the one demo by a girl with pink T-shirt). The only tools I need are two suction cups, 1 T10 screwdriver, 1 tweezer, I probing tool (I just used a paper clip) and a replacement power supply (I got it in Amazon). It's much easier than I expected and it took me only 45 mins to replace the PS. (I never fix any computer, no experience at all. Big thanks to that youtube video!)

The buzzing sound was completely GONE! Hope this info helps.

 

[keeper11]

Hi mine got fixed some how i took the advice
remove power cord waited 30 minutes, plug back
in booted and cross fingers no buzzing sound since
that was 2 weeks ago, very strange.
I was fearing trying to get a new PS here in
Denmark as there is no supplier here and if
i buy in USA get extra post and packaging costs
plus customs will want 25% extra.
So lets see if it comes back hope not.

 

[chscag]

Hopefully, your Power Supply has settled down and will remain quiet. Many times the buzzing can actually be caused by "dirty" power coming into your Mac. If the buzzing returns, you might try attaching your iMac to a filtered UPS (uninterrupted power supply). You should be able to buy one in Denmark from a store that sells electronic components. Otherwise, you can try ordering a new PS from Amazon.com in the UK.

 

[pm-r]

Hi mine got fixed some how i took the advice
remove power cord waited 30 minutes, plug back
in booted and cross fingers no buzzing sound since…

Basically by doing that you did a SMC Reset that can often fix a lot of goofy things.

Glad it worked for you and I have the same iMac model.




- Patrick
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