Noise problem with iMac...

[FMiguelez]

Hello.
Recently, my iMac (Snow Leopard) is making a weird noise when waking from sleep. It sounds as if the fans are going crazy to full power.

This happens when I have a loaded VE Pro instance (slave) and then put the machine to sleep. When I come back later and wake her up, it starts making the noise, and it doesn't stop. Then I have to shut down and power on again. Sometimes, the machine will start making the noise even after the restart.

It has started doing this only recently. It never happened before, and nothing new has been installed or altered.

Any ideas of what causes this, or how I can make the fans stop? Is this related to PRAM or some kind of corrupted preference?

Incidentally, this never happens to the MacMini with Lion...

[mikehalloran]

Resetting the PRAM would be the first thing to try followed by repairing permissions.

The temp control circuits in the newer 2010-2012 iMacs are very sensitive and everything must be perfect - especially the 2011/12.

There are Apple Diagnostic routines to run if setting the PRAM doesn't do it. The hard drives have heat sensors built in. There is a whole blog on OWC about these issues. Until recently, iMac 2011/12 hard drives only worked if they had the Apple ROM and you couldn't get them from any other source. There is a workaround but it is very recent.

2010 iMac HDs must be replaced by the same brand - WD with WD or Seagate with Seagate - for the heat sensors to work. You do not need the Apple ROM, however.

This issue is 2010 and newer iMacs only. Minis use 2.5" HDs without built-in heat sensors.

[bayswater]

Apple has some articles on this, and suggests resetting the SMC. The problem appear to be something to do with the Mac not knowing how hot it is, so running fans just in case.

http://support.apple.com/kb/HT3964?viewlocale=en_US

BTW, smcFanControl is a useful little menu app that reports temperatures and fan speeds and lets you control fan speed settings (but the general expectation is that you will use it to make the fans run more faster and more often, not slower or less)

[FMiguelez]

ThAnk you for replying.

I will read the article and OWC blog now.

Also, I should have mentioned that my iMac is a 2006 model. I increased its RAM to the max (6 GB), and I also replaced the HD a bigger and faster one (7200 RPM).

It definitely sounds like it doesn't know how hot it is... Waking from sleep it should be almost as cool as if I were powering it on.

[MIDI Life Crisis]

I have learned to NEVER let any of my machines sleep.

[mikehalloran]

Is the temperature sensor still attached in its correct location?

I don't know the 2006 iMac but Minis have them taped to the drive itself. Perhaps the tape is no longer holding or the sensor has shifted position.

[FMiguelez]

I have learned to NEVER let any of my machines sleep.

I never let my master computer sleep. It refuses to wake up and need to force a shut down causing all kind of problems with some preferences. I always assumed it was because it's an old G5. But then I got curious about the other machines and... well, it seems the iMac doesn't like that either...

If following the above suggestions won't fix the problem then I'll simply stop putting the slaves to sleep.

I am just trying to save a little power when I'm not actually working... but they are all connected to a couple of no-breaks, so I wonder if it actually helps

Is the temperature sensor still attached in its correct location?

I don't know the 2006 iMac but Minis have them taped to the drive itself. Perhaps the tape is no longer holding or the sensor has shifted position.

Uh-oh... I don't know....

I hope I didn't mess up that tape when I replaced the HD. But I don't think so, because it has never made any fan noise, except for now when waking from sleep (and it does not happen every single time).

I'll do the suggested tests when I get to the studio. If they fail, would I need to open the computer up again to make some exploratory surgery on it to check on that temperature sensor you mentioned?

[bad andy]

You can use the various iStat programs (I use the widget) to monitor the temp sensor and fan speeds in your machine. This is useful to determine patterns and correlations, and causes between CPU/temps/fan speeds.

http://www.islayer.com/apps/

Have you tried the aforementioned SMC reset?

[FMiguelez]

Hey, Guys.

I did the suggestions above, and for the past days the computer has not been making the noise anymore. But it didn't always happen, so I hope it doesn't suddenly start again...

Thanks for the ideas!