I just upgraded the firmware on my dual 2.26 quad-core 4,1 to 5,1 (anticipating upgrading to X5675s). No problems with the upgrade; the Mac now shows as a 5,1. But when booting up the fans rev up to full speed. They drop back down after about a minute but this didn't happen before the firmware upgrade. I tried a SMC reset but it didn't make a difference. I was going to see what reverting to 4,1 firmware did but got the 5770 error and didn't want to get into looking into that tonight - I'm going to have to stay with 5,1 firmware when I switch to hex cores anyway. Any help?