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I have a 2009 octocore Mac Pro. A few weeks ago it started making a constant noise. It sounds like a fan. The computer is not particularly hot. I checked with Temperature Monitor and CPUs/disks/etc. are around 40C. Only the Northbridge chip and sink are at 73C and 65C.

Is there anything obvious that my Mac needs or that might have caused the fan to get so loud?

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Resetting the PRAM took care of this on my iMac G5, not sure if it'll help an Intel mac. –  Neil Fein May 5 '11 at 22:03
    
Ta. I'll try that. –  Andrew J. Brehm May 5 '11 at 22:05
    
I looked this up, it's still advice Apple tells people. Will make it an answer. –  Neil Fein May 5 '11 at 22:11
    
You can use iStat Pro (islayer.com/apps/istatpro) to check individual fan speed and see if the problem is localized –  Agos May 6 '11 at 10:24
    
Mine is noisy, too, but the CPU fan (the noisy one) is only running at 500 RPM. Maybe it's just dirty and makes extra noise? –  user31314 Oct 5 '12 at 2:04

8 Answers 8

You can try resetting the PRAM.

There's more info on the Apple support boards , including further steps you can take if this doesn't work. Also, there's a thread about what settings will be nuked when you reset the PRAM.

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If anyone can replace these links with any Apple documentation that's more official, please feel free to do so; forum posts sometimes go away in a few years. –  Neil Fein May 5 '11 at 22:16

I'm a bit scared to admit this, but here goes…

We have a bunch of Mac Pro's in office. One of them (in a rather quiet room no less) started making a persistent high frequency continual buzz. It was definitely a moving components, because shutting the computer down would stop the sound. Tracing the sound eventually led me to the video card. Despite how low it was spinning, the video card fan was spinning nevertheless. When I would press my finger onto the middle of the fan (forcing it to stop spinning), the sound went away.

At that time the computer was highly highly mission critical, so downtime more than a few minutes was not a good idea. The Apple Store had none of our video cards in stock, and they were unwilling to take my word on the diagnosis and order it.

So, I engineered a 0.01¢ fix. I took a piece of scotch tape, and stretched it across both sides of the fan (the fan is raised with a plastic housing), and smoothed down the middle on the fan's plastic. The fan stopped spinning, and the sound disappeared. The office was quiet again.

Note that this is probably a TERRIBLE IDEA, because it restricts air flow across the video card which is a very hot device anymore. I honestly don't suggest this fix.

But, what I am saying is that you should check out your video card fans, and you can temporarily stop it to see if it resolves the audible issue.

And really, you can try this with every fan, not just the video card fan. Do be careful, however. Despite being plastic, some of these fan blades can hurt.

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I'd advise against stopping the fan completely, but it may be worth the effort to blow the dust out of the fan with (low-power) compressed air. You can even hold the fan blades still while blowing it out so as not to kill the bearings. That can help. –  user479 May 6 '11 at 2:40
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I said the same thing :). My solution is not a good idea in anything more than the short term, but the point was more to offer a suggestion of where to look for the noise. –  Jason Salaz May 6 '11 at 2:59
    
Sure, I'm not disagreeing with you. Just adding the bit about blowing the dust out. I can see where my comment might have been misinterpreted. –  user479 May 6 '11 at 3:00
up vote 2 down vote accepted

I don't know if this was really the solution but it seemed to work.

I opened the computer, took out the CPU board and blew the dust off it and the fans and the entire computer. Apparently that did it. Maybe I should do that once a year. The last time I cleaned the computer was last year when I put more memory in.

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There are quite a few heat sensors in modorn computers. If your computer thinks one of them has malfunctioned, it will assume the worst and run the fans full blast. This is annoying, but it ensures no components will overheat until the computer is repaired. Blowing off dust may have helped, but I assume you removed and reseated the fans in the process, and it may also be the case that the re-seating itself fixed a loose connection, and was the fix. –  username Jun 9 '12 at 11:31

In this Apple support article, Apple says that resetting the SMC can fix fans that are constantly spinning for no reason.

After performing normal troubleshooting, these symptoms may indicate that an SMC reset may be necessary:

Fans The computer's fans run at high speed although the computer is not experiencing heavy usage and is properly ventilated.
...

Here's what it says about how to reset the SMC on a Mac Pro:

Shut down the computer.
Unplug the computer's power cord.
Wait fifteen seconds.
Attach the computer's power cord.
Press the power button to turn on the computer.

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Also, I would verify that this is not the issue: http://macsaregreat.com/?p=63

I had an older Mac Pro that was constantly running its fan, and it turned out it was just a dusty graphics card. YMMV

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I had the same problem... fan running constantly in a Mac Pro. I checked all sorts of stuff, including looking into the housing. It was more or less dust free. The I realised that the graphics card (ATI Radeon 1900, I think?) had it's own fan BUT the intake to that fan was absolutely covered in dust! A solid wall of dust (even though, every 6mos or so I'd wave the vacuum around the computer). Once I pried off that layer of compacted dust from the graphics card fan, the machine is running silently!

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resetting the SMC worked for me.

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This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. –  bassplayer7 Feb 1 '13 at 15:11

After reading the responses I used my compressor to blow the dust out of my 2008 Mac Pro and it solved the whistling problem. I was also amazed by the about of dust the housing had gathered over the years. Thanks to all who posted responses to this question.

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This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. –  Rob Jun 5 at 6:03
    
Please don't add "thank you" as an answer. Once you have sufficient reputation, you will be able to vote up questions and answers that you found helpful. –  M K Jun 5 at 6:32

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