Buzzing Noise From Bottom of iMac

I had a Toshiba notebook before this imac and if I picked the power brick up and sat it on a hard surface it would make the same kind of buzz noice my imac makes.

That's fully in line with my yesterday's posting: the transformer is the source of 'buzzing', which you hear amplified because of the brick's having been placed on a sound reflecting board.

Just dont upgrade to Tiger, I did it today and the buzzing noise went into overdrive, Apple says its the fan and they will ship one out eventually.

I received my 20" Rev. A on Tuesday and it is now starting to make the buzzing noise. It is not too quiet and is tolerable when something is covering the middle of the bottom of the screen. I tightened all the user-serviceable screws around the power supply and checked the three case screws to make sure they were tight. When I started the computer up after that, I only opened Safari and came straight here. It probably started 30-45 seconds after opening Safari. It is the only program open and it is making the noise. I put a layer of 5 or 6 Post-It notes over the middle-bottom and it is just a regular fan noise now; you can only hear the buzz if you try to. Definitely not whisper-quiet, but tolerable for the moment.

I talked with Apple support online and we discovered that my buzzing noise is the fans and not the power supply. The culprit was running Virex on Tiger... apparently it causes the CPU to run fully all the time. After uninstalling it, the fan noise considerably decreased, and my CPU temperature went down about 20º F. The fan was running about 4000-some RPM and is now down to 1500. However, I was also told that this noise was "normal". It sounds like a model airplane engine, which I would think is not normal. Hopefully from now on the fans won't kick into overdrive until I have a whole bunch of apps (8+) open. While I am sure the noise will come back with stress on the processor, I am glad that it is not the power supply that is making the noise.

Once again, if you are running Tiger and have Virex installed, it is making your CPU run harder than it should.

Ed,

Are you certain about the fan locations? Where did you find this information?

Thanks,

Shawn

What is the PSU?

I get a continuous high-pitched buzzing sound coming from the bottom left of machine, which is not far from the Apple logo.

Sound intensit varies a bit, but is always there, and is only over-shadowed when the fans go nuts. So I get either a high pitched buzz or loud fans.

this buzzing noise problem has existed since the flat panel imac first appeared last september. these discussion boards have been full of this subject and the only solution that sometimes works is replacing the motherboard. but only sometimes.
in my case i cannot play dvds because the buzz is so loud it interferes with the sound from the dvd- even across the other side of the room.
equally when using itunes there is a constant high pitched buzzing from the bottom left of the computer that never goes away.
I have contacted applecare and they say they are waiting for a solution from Apple...
and i'm still waiting after 6 months.
why can't they fix this? why are some lucky and get silent imacs and others not?
why don't Apple have the decency to admit their fault and fix our computers?

PSU = Power Supply Unit.

It is located on the bottom left when looking at the front of the unit. If you adjust the brightness of the display and the pitch changes, that could indicate a bad PSU.

Anyone thinking about covering the bottom vents of this computer should consider the fact that this is where cool air enters the computer. It sounds like a recipe for disaster to me.

- Shawn

PS: By using my stethoscope and BRIEFLY disconnecting each fan I have traced my excessive fan noise to the SYSTEM fan on my rev B 20" and am planning to request a replacement fan to see if it solves the problem.

Shawn:

By system fan, you mean the large open one that is on the left while looking at the back of the computer?

Emm, I received my Brank New iMac 2 days ago and this buzzing sound come out and never go, after reading all the pages above I believe it is that I got a PSU problem as the sound still exist as I shut down the Mac, only go away with power supply cut, god. apple care told me it is normal, how can i sleep with this buzzing,....(donot bored to cut power supply everytime...)

Ed,

Yes, the one with the turbine visible is the system fan (at least on the 20"). The CPU fan (the enclosed one next to it) makes a little noise too but not nearly as annoying.

- Shawn