Buzzing Noise From Bottom of iMac

My imac is making buzzing sound as well, i think is the fan

I install the aquarium screensaver and let it run, after a while the sound came out, it was just noisy. it sounds better after i restarted it, but did not get back to the silent stage that it used to be.

my imac is only 5 days old, first with LCD problem, then is the noise.

should have bought a power mac instead...

ready for some voodoo? Try this ...

Put your hand under the screen on the left hand side. Did the buzzing disappear?

I got my Imac last October and was initially totally freaked out by the buzzing. I'm never home when AppleCare is open (in Australia) so I've been reading these posts regularly - all the midplane replacement etc scared the ... out of me.

What I noticed was that if I put my hand under the air vent (try blocking it completely) on the bottom left the noise disappears ... I'm not into physics / sound dynamics but if I hold my hand 2 cm below the opening it gets even louder (as the sound 'bounces off my hand) ... so were did this leave me - two things.
1. I have a bit more mess under the bottom left of the screen (not too hard on my desk) and the noise drops significantly
2. Get some nice head phones, a good cd or two, a glass of wine and the noise goes away completely!!!

My 20" I purchased in February has had a buzz from lower left since day one. To me it's acceptable since it's pretty low. I can hear it from about 4 feet but barely and only since I'm trying to hear it. It does get louder occasionally when I'm downloading or running an app, but not by much.
I tried the "hand under the lower left bottom" trick (others have suggested it) but it didn't work for me. I, too, think it's a fan since that it where one of the fans is located. If you plce your hand lightly on the lower left rear of the machine you'll feel a slight vibration, but not on the right side. That's your buzzing.
I personally don't feel this is a "defect" or hardware problem. No computer is absolutely silent. This iMac is a state of the art leading edge technology. I'm happy with mine. Accept it and you'll hardly notice it after a while.

have you talked to apple technical support?

Sal -have the same issue! On my second G5 and they came out and replaced some parts to no avail. Buzzing is driving me mad. I know this is not a fan and would love to just switch out the part if I knew which one. Please tell me if you have had any luck

the buzzing fan is the CPU fan in the 20" model (it's faced down and the heat wears out the bearings faster than otherwise-that's the buzzing you're hearing); the 17" models' CPU fans are at the bottom.

Anyway, if you're sure it's not fan noise, here's a way to find out definitively: Raise and lower the screen brightness (F14/15) while observing the noise, and if this affects the buzzing noise, then it's your Power Supply. Otherwise, it is fan noise.

My iMac's Hard Drive is sitting on my desk right next to the iMac in an external enclosure, and the sound it makes isn't a buzz, but a slightly scraping sounding whir. I've put it back into the iMac before to see the difference in fans, etc., w/ and w/o the HDD inside, and I can say that when it was inside, I don't hear the HDD. And yes, the HDD does make an occasional buzzing sound when it's really hot, but I don't hear this when it's inside the iMac, and like I said, it's an occasional buzz.

Sal D

What everybody is taking about is not the HD but the PSU.
I replaced my midplane and PSU on my 20' Rev A iMac.
The PSU is located behind the apple logo. That’s were the wire goes into it. Makes sense.
The HD is located in the upper left.
Usually when the HD goes it sounds like a clicking.
The buzz is the PSU. I replaced mine myself.
It took 15 min.
Until you replace the PSU - I recommend don't put your iMac to sleep. They burn out sometimes in that mode.
Order a new PSU – it’s easy to replace it yourself.

If your attempting this, one thing I did that eased things a little was to turn one of the back panel retaining screws back in – the one in the middle under the foot. This pulled in a little bracket leaving more room for the power supply to slide in. Just remember to unscrew it again before replacing the back panel.Good Luck

Actually, in my experience there are two buzzing sounds that could be coming from the bottom of the iMac. The first is a either a droning whine/hum that is heard on the lower left...this appears to be a defective CPU fan. The second is a buzzing sound (like a phlorescent light bulb) that is comming from the lower right...this appears to be a defective PSU. For some people this second noise can be affected by raising and lowing the brightness, for others (like myself), it can be affected by moving the right hand scroll-bar of an open window up and down quickly (sounds like a lightsaber). The only way to make certain which part is a the culpret is to take the back cover of the iMac off, turn her on and listen to both areas closely. I've had both of noises since getting my iMac last fall and have felt it was not worth the frustration of dealing with AppleCare who apparently continue to tell us that it is within spec. Good luck.

I get the buzzing sound when theres a power outage and is using the backup UPS

so i guess its something to do with the electricity

George

The UPS is supposed to make a noise to alert you it is working. Like a beep beeep
I hope you are shutting down your iMac – when you are having a power outage.
You never know how long they will last. Beeter you then a loss of power.
My last power outage lasted 1 minute.
I couldn’t believe it.
So I decided to keep my iMac shut down for the night.
You never know when a new storm will come by and knock out power again.
I pull the plug also.
It’s good every so often to have a cold restart for the system.