"24V DC Cooling Fan" The higher the speed, the greater the noise. If the non-prolonged abnormal noise, then that in itself is not a problem. The reason that the fan noise after another, from the temperature-controlled cooling. When the "24V DC Cooling Fan" tasking frequently, the temperature will gradually, will take the initiative to enhance the speed, and thus play a cooling effect. Strength of the human ear to hear the sound, actually sounds with frequencies vary, such as "24V DC Cooling Fan" 1000Hz particularly sensitive when the human ear, so the two different frequencies of the same sound pressure will avoid frequency of 1000Hz its volume is large. The difference between the so-called noise and music just sounds comfortable or not, and no two sonic terms.