Get into your BIOS and DISABLE anything like EIST (Intel Speedstep Technology) and C1E. These 2 items adjust your multiplier and voltages to throttle down your CPU when it is not being fully utilized. Disabling these things will keep your CPU clocked at top speed all the time.
Sorry, I misread your post. Thought was CPU throttling not fan. Listen to dadiggle and also make sure in your BIOS that Quiet Fan is disabled so the board won't throttle the fan.