Hi-

It could be a faulty temperature sensor. Since your iMac is a month old, it's still under warranty, so take it to an Apple Store, or contact Apple Care, and have it checked out. Good luck.

That's good to know. Perhaps there's an automatic power reset on the new iMacs when they're unplugged for a while. That would be nice for those of us who have had to reset the power manager on our machines.

Glad to hear your fan problem is fixed. It's interesting to hear about some of the high-tech solutions recommended by Apple. Good luck.

Hi, my iMac Intel 20" does the same thing. Sometimes, when I turn it on (and don't hold the power button until hear the beep) the fans go crazy!!!! Strangely, this only happens when I don't wait for the beep to release the power button.

And the problem is: when I use BootCamp and the fans are crazy, Windows don't start. MacOS X runs OK (if you can ignore the noise and the "tornado" on the back of monitor..). Go figure....

Anyone has the same Windows problem??? It only crashes at startup when the fans are like that, so i guess it's no a software problem.

Dude I want to thank you so much. I did exactly as you said and puff the fan noise went away. I was going nuts.

Hello. Just purchased a 24" alu iMac refurb (2.4ghz 2k7 model.) Is it normal for the fan to run 24/7?

It's still fairly quiet. It just runs constantly at 1200 rpms (cpu and hd fan) and 700 rpms (optical fan,) and is loud compared to my old 20" aluminum iMac 2k7 refurb which was dead silent with no fan noise at all.

After some internet searching it looks like some say their 24" iMacs are dead silent while others say there is a slight fan noise to theirs.

Apple had me power it off, unplug and hold down the power button for 20 seconds, but that didn't do anything. Apple tech support said the fans shouldn't kick in at all upon bootup if the iMac has been off for a few hours. But the fan always seems on.

A friend says he puts his ear up to his 24" alu iMac and hears nothing.

What say the MacWorld 24" alu iMac owners?

I have purchased a new iMac 24 inch (mid 2007 model; 2,4Ghz; upgraded to 4Ghz of memory) six months ago. Everything seemed fine until about a month ago when I have noticed a rattling noise coming out from the bottom left (where memory slot is located) which drove me nuts. I have tried to fix this problem by restoring the SMU (System Management Unit) however; this option did not resolve this issue.
Then, I have decided to run Apple Hardware Test from the internal hard drive by restarting my computer while pressing and holding the 'D' key on the keyboard during startup. (http://support.apple.com/kb/HT1883). This process was completed in a few minutes and once I have restarted my iMac, very annoying rattling noise was GONE!