I just purchased a used 2008 Mac Pro (2x2.8GHz, 8 core). When I tested it out with the seller, I didn't notice that there was a lot of fan noise (we were in a server room). When I got it home, I really noticed the noise. After a lot of troubleshooting, iStatMenus shows that the IO/Expansion fan is running at 2900 RPM, which is the max speed. As soon as the system starts up, this fan soon goes to max speed. The system does have an upgraded video card: the ATI 4870. I have thoroughly cleaned the system out (dust, etc.). I have checked for any loose temp sensor connections. Apple Hardware Test does not show any errors. What else should I check? Thanks!