Buzzing Noise From Bottom of iMac

BTW, here's another example of noise recorded with the internal mic:
http://homepages.nildram.co.uk/~smelik/mybuzz.mp3

That sounds like the fans are spinning too high. But listen carefully - you can hear "my" buzz underneath it!

When I have nothing running except X Resource Graph (and Drop Drawers), for 10 minutes, the CPU is 2900. Starting Safari means a hike to 3500, then a decline to 31-3200. Starting iTunes, DT Pro and Preview, back to 3500.

Even then, not using it will slow it down to below 3000. Starting Classic means a hike to 4200.

But when I'm at work for a longer period, it hovers around 5400-5500.

I'm still not clear about the relationship between CPU fan speed and noise. If, as I udnerstand now, a normal CPU fan would stay in the 1500-2500 bracket, would that mean that a replacement fan would solve my noise problem?

smolk,

I think any iMac is going to be noisy at those fan speeds. What are your temps? My guess is either you have a hardware problem giving you high temps or some application in the background doing the same thing.

Even brand new perfect fans will make noise at your present speeds.

John

Smolk,

How hot is the room you are using your Mac in? I have noticed that these machines are extremely sensitive to ambient temperature. Anything over 80°F and the fans kick up fast.

- Shawn

I have no thermometre; X Resource Graph provides a temp of 66F for Luton (I live in North London). My study is small, though.
At the moment CPU is at 3600 with the following temps:
CPU T-Dio 150.1 F
Hard Drive 128.3 F
I would be surprised if ambient temperature is the problem, although fresh air is sometimes a problem. Humidity is 60%.

a new fan won't solve the problem, I got it replaced twice and mi imac is still buzing...

excellent link...but I still hope Apple will find a solution for this...

smolk-

I had similar fan speeds on my 17" imac G5 rev A. Found that resetting the pvram fixed it. May want to try this if you have not already. I copied this from a previous post:

Resetting the pvram (Corrects problem wit fan speeds)
Imac G5

1. Reboot your iMac, and as it restarts press and hold Apple + Alt + O + F. Continue to hold until a grey screen appears with text telling you you can release the keys.

2. Type in:
reset-nvram <Enter>
reset-all <Enter>

3. When the login screen appears (or you are logged in automatically), restart the iMac. Don't do anything else - don't run any extra software and especially don't restore any configuration options that have been undone by the nvram reset.

4. When the login screen appears again (or again you are logged in automatically) shutdown the iMac. Again avoid doing anything else.

5. Take the back off the iMac, and press and release the lower of the two buttons (centre near the top, under the middle fan) firmly. Maybe do it again for good luck.

6. Put your iMac back together and restart.

probably a deffective PSU...

Well, yesterday the iMac starting behaving weirdly. One Classic app refused to start up, and another behaved in strange ways. And then the computer almost froze. I was desperate, writing a speech for the evening which I had neither saved nor printed, so I wanted to avoid a restart. It took ages for the OS to force quit some apps. When after 1,5 hour I managed to quit all apps one by one except for Ulysses (in which I was writing), I saved and printed right away.

I then did the Apple Hardware Text. No problems found. I then left for my wedding.
This morning the iMac did not start up: screen turned blank after the initial Grey screen with the wheel on it (not the MacOS window).
So I restarted with the TechTool CD, and it found problems in Volume structure. It is now repairing them (already for 1,5 hour, after a quick start it now goes through 2,626,512 steps by 3 steps a second).

I do not know what is wrong, but I'll sure need to check this out.

Re PSU, I had understood that a good indication of a faulty PSU is to turn brightness swiftly up and down and see whether the fans react. They do not. So I assume the PSU unit is fine. Or the test is not a reliable indication.

Actually smolk, to test for a defective PSU you change the brightness up and down, and listen for the buzzing to go up and down with the brightness. If the PSU is the problem, then the PSU is causing the buzz, not the fans.

yes, well, there is no change in the buzz when I move brightness up or down. At least there wasn't. I don't get that far anymore: After Apple Chat and various runs of verify / repair disk, there are errors which cannot be repaired and the system now hangs on the white on blue window Mac OS X / Starting Mac OS X. I'm advised to go to an Apple Service centre in London. Any advices anyone? (North London) I have dealt with Albion in the past, but of course this computer was purchased directly from Apple on the Apple Store

The buzzing noise you're reffering to is a problem im told apple are aware of and if u explain it to their technicians theyll gladly take you're mac in to replace the faulty part which, by the way is the power supply. ive had this replaced on my 17" 1.6Ghz iMac and the noise had receded but is not completly gone but its much more managable. When my iMac was in for repair they also replaced the logic board but that did nothing so i hope this has helped!

I hope you are not using the AppleCare version of TechTool. It is not Tiger compatible.

- Shawn