Hello, I've got a RevB iMac G5 20" (1.5 GB ram) for a year and a half now, and since the last six months, the fans becomes quickly really loud for no apparent reason. It seems that my iMac think he is an helicopter and he want to take off by spinning it's fans the fastest it can. This is really annoying and it was not like that in the begining. It prevents me from doing audio conversations: the fan are so loud they make it impossible for the other to hear something else than my fans. Try convincing your friends to "switch to mac" with noise like that during an audio conversation! Sometimes just with firefox running I have my fans spinning really fast, with no intention of stopping anytime soon. To give you an idea, i use iStat pro for checking my fan speed + computer temperature and there is NO correlation. My fans are reaching 4400 rpm and sometimes 6500 rpm without anything CPU intensive running. Just using skype will make my fans go crazy in less than 10 minutes, while the temperature is not high (<60 C) inside the computer and the CPU usage is almost nothing. And once they are started, they will stay like that for a long time (hours) even if all applications are closed, except finder and dock. I'm sure there is something wrong with the sensor since when I reboot, the fans become quiet again for the same temperature. Now, coming from the windows world, I'm used to reboot but I sure the must be another way... Booting every 10 minutes to keep my fan noise low is not my idea of fun! If I only put it to sleep and I wake it up after 5 minutes, the fans will continue to spin at high speed and make the same noise as before. I've tried the reset the SMU (http://docs.info.apple.com/article.html?artnum=301733) but it does not seems to have made any improvement. I've seen other threads on this but only with Rev A iMacs G5 (http://forums.macrumors.com/showthread.php?t=101447). I've tried also the tips about setting the energy saver preference to something else than automatic but it's not helping either. (http://www.macosxhints.com/article.php?story=20051106063023177) Anyone has any suggestion before I open my iMac and simply rip the fan out? Thanks.