I received my late 2006 17" iMac yesterday and am absolutely chuffed with it. However, OS X is handling the fans in a very odd way; I downloaded smcFanControl (as I do on every Mac I own) & was looking (& listening) to the fan sensors. Idling, the ODD & HDD fans are at 4000rpm, whereas the CPU is only at 1000. It's making quite a noise. Then, when I boot into XP via Boot Camp, every is silent, even when playing a pretty intense game. Is this natural? Are the fans automatically defaulted to a higher RPM in OS X? I'd just like to find out if it's a software issue before opening him up & taking a gander myself. Thanks.
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Loud Fans - Only in OS X?
- Thread starter Goftrey
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Have you tried an SMC reset yet?
Intel-based Macs: Resetting the System Management Controller (SMC) (Apple Support Site)
Normally the HDD and ODD fans are idling at 900 to 1,200 RPM in an iMac.
Normally the HDD and ODD fans are idling at 900 to 1,200 RPM in an iMac.
It's not truly idling then. Open Activity Monitor, set it to show all processes and sort by CPU%. Something is making it work.
Okay, I just installed Fan Control & found the base rpm is set at 3500rpm. So I set that down to 1000 & have been doing various stress-tests while keeping an eye on the temps. The iMac is now dead-silent & none of the temperatures have shot up at all. Little bit weird but everything's all good now. Thanks for the replies 
I know this is totally unrelated, but on my iMac (a 2010 model), the fans only get noisy in Windows, when playing video games. And even then, it's not load at all. I wonder how this is related to the significantly superior performance of games in Windows compared with Mac OS X...