iMac's fans make awful noise

Question

My iMac's fans are making an awful lot of noise, sounding like a piece of cardboard is in them. It's a kind of ticking noise. This is happening since a few months ago. I have not changed any hardware. I have never encountered any other problems with my iMac and it has never crashed. My Mac is running normally and fast.

Here is what iStat says:

I have an Intel iMac (iMac9,1), Intel Core 2 Duo @ 2.66 GHz, 2 GB RAM, running Mac OS X 10.6.6.

I have tried to reset the SMC but this did not help.

How can I make this noise go away without opening my iMac or sending it back to Apple?

Answer 1

Your fans are running at speeds appropriate for that model. Even using a stethoscope on the rear of an iMac, good techs have been confused between hard drive and blower noise unless you can change the noise by increasing or decreasing the fans or the HDD.

Rhythmic blower ticking is one of two things:

1. Failing or failed bearings in the blower.
2. Foreign object (paper, hair, other) lodged in the blower.

Choice #2 is less likely since the airflow around the unit usually precludes things getting stuck there. Also the design makes it unlikely things large enough to make noise or stick can enter the blower area.

I wouldn't recommend shaking an iMac (running or not), but tipping it on a side or upside down with a friend's help and then powering it on would let gravity and the airflow dislodge all but the most unlucky piece of debris from a blower. Be aware that succeeding to move debris may land such debris in a worse place than a blower, so do use caution.

If the bearings are the cause - you might try a fan control software to run the fans faster (sometimes higher speeds are less noisy) but do get ready for a visit to the shop as bearings don't fix themselves and the noise will get worse as it wears. A technician is the best person to get debris out and truly resolve a ticking noise whether it's a hard drive, optical drive or a blower.

Answer 2

I haven't checked to see if smcFanControl will work with your particular mac, but I have used it for several MacBook (pro and consumer) and even on my desktop tower mac (all intel) to control the fan speed. For example, when I was playing WoW in full-screen mode, I would increase the fan speed manually to keep the temp down and then reduce it when I was done. It has a nice menu bar widget that shows the current RPM and temp.

You might be able to use this widget to manually set the speed lower to reduce the noise. I would recommend you try to further investigate the cause of the issue so that you don't inadvertently burn out your computer. One activity you can do to narrow down the cause is when you see/hear the fan increase in speed, check your Activity Monitor application to see what is taking the most CPU. You will find this application in your Utility Folder. Once launched, use the popup to see All Processes and then sort by %CPU column.

Good luck!

Answer 3

If there is a "ticking noise" when the fan runs, then I am willing to bet you have an object of some kind that somehow got stuck against the fan and the fan blades are hitting as they rotate. Crack open the shell and give it all a good blast with some canned air. But, if it's not something visible, then I would say take it to an Apple Store.

Answer 4

These are all good ideas so mine is just a shot in the dark. Try vacuuming the vents along the bottom of the display. The loose item may pull clear if there is one and worse case, you've removed some dust and the fans may not run as often.

Answer 5

Well, granting you haven't restored your OS, you should still have the Apple Hardware Test on your system. Give that a whirl and see what it comes up with. http://support.apple.com/kb/ht1509

Answer 6

Have you been excessively playing games/running the Fan before that? I had the problem of a rattling Fans as well on a MBP, but it started quite subtle and then went on to sound as well like a piece of cardboard. However it was not related to anything beeing stuck in the Fan, but it was simply the lubricant dying. So I went to Ifixit.com disassembled my macbook. I was also able to disassemble the Fan by opening the screws on it, and pulling out the rotor. Then I cleaned the rotor shaft and applied silicon oil to it and put it back in. (I tried other oil as well but it would not work like silicon and the fan would start to rattle again (motor oil, "special" electronics oil, etc))