"24V DC Cooling Fan" different tone sounds only pure wind noise of the wind, and abnormal sound is different, when the fan is running, in addition to the wind, but if there are other sound, you can determine the fan has different tone. Abnormal noise may be due to the bearing of a foreign body or deformed, and improper assembly of a collision, or the motor winding is wound unevenly, resulting in loose, are likely to produce different sounds. "24V DC Cooling Fan" of life refers to the life of the fan radiator working time between failures, high-quality products can reach tens of thousands of hours of life in general. Under the price and performance of similar cases, choose a long life "24V DC Cooling Fan" clearly more to protect our investment.