If the CPU is not sufficiently cooled, the fan runs at high speed. To eliminate this drawback sometimes only need to re-apply CPU thermal grease. Remove the cooler, remove the old layer of thermal paste and apply a new one.
Higher rpm's may be caused by technical malfunction of the cooler. Standard fan in low skilled Assembly wears out quickly. In addition, the wear can be caused by a long lasting fan. To prevent wear, the cooler is subject to periodic cleaning and lubrication. If these steps do not help, you will have to replace the fan to a more modern model.
To reduce the speed of the cooler software. There are special utilities (such as Everest), through the installation and configuration where you can control the rpm of the cooler. Keep in mind that a weak model of the fan can still run at higher rpm due to the possible overload of the device and the CPU overheating.
One of the most effective ways of reducing the number of revolutions of the cooler – installation of additional cooling on the back of the computer. This will help to improve performance and eliminate overheating of the components of the system unit.
Another method involves adding to the power circuit of the fan of the additional resistor of 30-100 Ohms (for 12V circuit). Thus there is a risk that will increase the required starting torque, and the fan may not start when you turn on the computer. To solve this problem, connect a resistor parallel to the capacitor on the 500-4000 UF. If power is turned on, the fan voltage is 12 V, which then drops to the operating voltage of 6-8 V, limited by the resistor.