Did you check your settings in your BIOS? With AMDs, they have an option called Cool n' Quiet. If you turn this off for those chipsets, it will run the CPU at full strength the entire time which means your CPU may run at the hottest temperature the entire time. Cool n' Quiet will throttle the speed of the CPU based on the activity that is going on with it. I think with Intel they have something like that called SpeedStep which does the same thing.
Have you also monitored your ambient temperatures in your case? Maybe you don't have good air flow through the case so the internal temperature in the case is running high and causing the CPU fan to run faster?
Sounds to me as though the CPU Smart Fan option in the BIOS is disabled. When disabled, it runs the CPU fan at maximum RPM constantly. With it enabled, it will throttle the fan speed as needed when it heats up. For 3-pin fans such as this, use the Voltage option, not PWM. I'm not familiar with ASUS Q Fan... Perhaps ASUS renamed Smart Fan to "Q Fan"?
You'll want to be sure the fan is plugged into the proper lead on the motherboard. The correct lead should be a 4-pin one labeled CPU-FAN located near the very top of the board by the first memory slot.