Hello everyone, For the past couple months or so, (maybe starting around January) the fans on my iMac have been really loud for some reason. It's mainly the fan that's in the bottom left corner, if I put my ear up to it it's really loud, sounds like sitting inside an airplane while it's taking off. I use Bootcamp with Windows 7 Ultimate x64. It happens every time my CPU usage goes over 15%. So basically every time I play a game, even if it's not that intensive especially considering the decent hardware inside this system (i7, 5750) the CPU fan goes up to 4000 RPM, even when I just leave it for a while on the pause screen! I've installed Speedfan to check the temperatures: HD0: 58C Core 0: 55C GPU: 212751C (it must be broken or something) Core 1: 53C Core 2: 56C Core 3: 52C Using iStat Nano to read the fan speeds, I'm getting approximately: Fan #0: ~1000 rpm Fan #1: ~1500 rpm Fan #2: ~3500 rpm I can control fan 0 and fan 1 speeds but NOT fan 2 speeds. I've tried SMC reset and all that. This problem is pretty surprising for me since my iMac fans have been fine for almost 1.5 years (mid-2010 edition) and now the Fan #2 at the bottom left (at least that's what I think is making the noise) is really loud! (EDIT: I confirmed it's the CPU fan using iStat nano on the OS X side since it gives you the name of the fan) Could it be dust or temperature sensor problems? When I expanded the memory from 4GB to 12GB a couple weeks ago I found a lot of small dust ball things on the inside of the memory panel cover (so I couldn't see it when it was actually screwed into the bottom of the iMac) and around the tips of the memory sticks (not inside the slots but around the entrance things). Also my GPU temp readings seem broken according to Speedfan but on iStat they work fine. If anyone could help me sort out this issue that would be great. The incessant fan noise is getting on my nerves! I would really appreciate your help.