27" iMac Hum Resolved
 

My wife's new 27" iMac was producing a noticeable and annoying low frequency humming sound. At first I thought it was coming from the screen, so I shut that down. The hum persisted. Then I put the iMac to sleep. The hum went away. It came back as soon as the iMac woke up. I had visions of hauling it down to the store for a genius bar appointment, etc. Then I turned the iMac around and put my ear to the back of the case to try to isolate the area where the hum was originating. Imagine my surprise when I didn't hear any hum at all. At first I was confused by that. Then I gently picked up the iMac, lifting it off the counter top on which it was sitting. The hum immediately ceased. The hum came back as soon as I set the iMac back down. So it wasn't an electrical hum at all, it was a hum produced mechanically by vibration propagating from the iMac to the glass counter top. The glass was humming. I put fairly heavy felt pads on the bottom of the iMac stand, and the hum is virtually gone. It's no problem any more. And, I'm sure that a more sophisticated vibration dampening solution would eliminate the hum altogether. Just wanted to share the information.

Very interesting.
Does it matter what apps you're running or does it do it with no apps at all going on?

No apps, just Finder running.

Brilliant! Had my new iMac for just over a week when I noticed this low-pitched annoying hum. Didn't remember it being there when I first booted up. Anyway, checked lots of threads here and was on the verge of reluctantly returning my machine when I came across your post. Tried lifting the machine as you describe and it went! I have a hard floor and desktop and the sound was entirely caused by reflected vibration. Have just put some felt feet under the base and it's now virtually silent. I see Amazon also sell cheap 'vibration-free feet' for exactly this purpose. Thanks for posting your solution, you certainly saved me considerable time and trouble.

Thank you, thank you, thank you! I lifted my iMac 27 from the table, and the humming disappeared!:)

I just fittet some sound isolating felt from an old PC to the bottom of my iMac stand, and it removed 80-90 % of the humming :-)

Thanks for you great tip :-)

Oh what a relief!! This worked a treat...

I had this exact problem... annoying low pitch humming noise...

I've put my iMac on a marble chopping board (!) and its worked a treat. No sound at all now!

:-D

iMac hummm
 

I want to thank you!! Looking for an answer to another issue I came across your solution and bingo! My hum gone!!:D

Hello,

I would just like to confirm I have exactly the same humming low pitch very anoying noise in my 27" iMAC. I5, 12GB RAM, 1TB HD.

I fat book and rubber vibration absorbers under iMAC stand helped a bit but that's not really a solution. I wan't a silent computer. With Apple and 21 cent. I though I might finnaly get lucky. NOT!

Now it's reading laws, returning to store, talking to service people,...