The power supply fan of my Mid 2010 Mac Pro spins up after a few minutes since I installed 10.9. There is no real activity, only Safari and processor usage is very low. Power usage is about 96W reported by Hardware Monitor Light. Temperature Power Supply 1 & 2 are 25°C so no reason to spin up the fan. I tried resetting the PRAM and SMC but no result. On ML the fan speed is normal. I do have a GTX 680 (flashed) installed, connected to an external power supply. Am I the only one with this problem? Any suggestions on solving it? I did an update of 10.9, not a fresh install.