BIOS settings are usually something like:
AUTO, PWM and Voltage
Get a CPU stress test program (google) and see if you hear a CPU fan speed change (should be very obvious). If it doesn't change under stress then it's already at 100%. In that case, you need to try each setting. It's either PWM or Voltage (Auto just guesses). If it's on PWM then choose Voltage on vice versa.
You can buy non-stock HSF's with 120mm fan (good ones are $40), but only get one of your CPU fan is changing speed and it's still too loud for you.