*Note: many computers have a setting in the BIOS to turn on automatic fan control. It varies between computers (some have none). If you DO have it you must have a proper fan plugged into the proper CPU fan control spot on the motherboard AND have the BIOS set right. Mine was set to "AUTO" but my non-stock fan actually needed "Voltage" set to work.
If your fan control doesn't work right it will spin to 100%.
If you decide to purchase a better heatsink/fan combo you should see if you have motherboard fan control. If you don't, it might be best to get a LARGE heatsink (measure carefully) and put on your on VERY LOW SPEED/NOISE fan.
A $40 heatsink/fan can make a huge difference in how much your fan speeds up and how much noise you hear. My fan never even comes on unless I'm stressing my CPU (i7-860).
Example of a proper fan setup:
1) 120mm fan (front, bottom, constant RPM, VERY LOW NOISE/SPEED)
2) 120mm fan (top, rear, constant RPM , VERY LOW NOISE/SPEED)
3) 120mm fan (CPU heatsink, RPM varies. Hardware control. set in BIOS)
4) 120mm fan (PSU, RPM varies; controlled by PSU)
5) Graphics card fan (RPMS varies; controlled by graphics card hardware)
*Note that there is a dual method of setting up proper air flow:
1) Fan speeds vary CLOSEST TO WHERE PARTS GET HOT (like the CPU or GPU)
2) Fan speeds remain CONSTANT to maintain overall case air flow ( in general, from bottom-front to top-rear)