Buzzing Noise From Bottom of iMac

I have a very similar buzz.

Of course, since I hate noises and figured Apple wouldn't do squat, I fixed the matter on my own:

I opened up the machine. I noticed that the center screw that holds the lid on did not completely force itself against the metal plate opposite it. The resulting vibrations caused that annoying little buzz. To fix it, I took some paper and some tape, folded the paper up and stuck it between the screw and the metal plate. I screwed it in and made sure it was secure. I then covered up the iMac and used the tape to further tighten the cover to the machine. That got rid of the noise.

Convoluted, sure. But it worked.

I know about the UPS sound
but i also hear the buzzing sound while the computer is using the backup power from the UPS
So its possible that the buzzing sound is connected to the electricity

And lol one minute power cut
we have power outages which sometimes comes to an hour

Are you stating that with changing out the PSU your iMac is completely silent when the room is quiet, regardless of the tasks you put it through and the obvious fans that come on when the processor is being worked? Were you able to call Apple Care and request a new PSU? Or did you have to prove to them it was having issues?

yeah, I thought mine was fixed with a software deletion, but no. It's loud as ****. When I'm listening to itunes, I hear it over the music in the next room. Apple is really trying to dodge an embarrassing mess here. The best thing for them to do is fix it before it tarnishs their rep.

Librate:

On the 20" model, the CPU fan is the covered one at the top. The HD fan is the once at the bottom.

Well, I have only had my iMac for 6 days now and I'm just probably being a little paranoid, especially since I have been perusing the discussion boards since March. What I hear is a very slight buzz that's only evident when there is absolute silence in the room. I does increase ever so slightly when I am switching back and forth between profiles, which is so freakin' cool when it rotates back and forth. I don't hear it when I'm listening to music, regardless of what kind of work I put it through. But, like I said, after reading through the iMac discussions for the past couple of months, I am looking for any signs that would show me my computer has an issue, which is probably over doing it. My wireless keyboard didn't want to start properly when I first took it out of the box and has issues whenever I leave it on but turn off the iMac, but other than that, everything has been honky dory. Anyway, I saw this post and it seemed similar to what I was hearing two nights ago, but I turned it on this morning and it didn't sound as loud as I thought it was. I'm probably worried about nothing, but I'm also trying to make sure that I don't overlook anything. Does any of this make any sense?

iLaurence

OK Dan, yours seems that most logical and quick fix solution.

I'm gonna give this a go to stop that little pesky noise.

Sal-

That sounds like your Power Supply is the issue.

Yes, Edward, I'm well acquainted with the 20" model fans. I believe you misread my post - I was comparing/contrasting the locations of the CPU fans between the 20" & 17" models.

At the moment most of the noise seems to come from the HD.
If you want to listen to the factory inside, try to get an ear (I suggest your left)
next to the discdrive. (grrr)

Having read all the messages produced so far regarding this subject, the only conclusion I can come to is that the transformer in the PSU is the basic culprit.
All transformers do 'buzz', with a 60Hz frequency in your case (plugged into the AC outlet, which provides 110V, 60c/s electric power.)
That all transformers buzz is the result of their construction. If correctly designed and well built, one hardly notices the noise. But, they do produce noise, and dependent on where and how they are placed and fixed, the noise becomes more or less noticeable, sometimes even 'amplified' as a result of resonance.
What can one do? Delve into the spot where the transformer is located, tighten any screws you might encounter, check whether metal or plastic parts might be vibrating, and if so, try to somehow introduce some material (a match, a piece of cardboard, some chewed chewing gum, and the like) in such places where it might dampen these vibrations.
Good luck!

QUOTE:

"What can one do? Delve into the spot where the transformer is located, tighten any screws you might encounter, check whether metal or plastic parts might be vibrating, and if so, try to somehow introduce some material (a match, a piece of cardboard, some chewed chewing gum, and the like) in such places where it might dampen these vibrations."

LOL Chewed Chewing Gum. That's original. 🙂

iLaurence