"24V DC Cooling Fan" noise and friction, air flow related. Fan speed, the greater the amount of wind noise will be greater due to another fan's own shock factor can not be ignored. Of course, high-quality fans will shake itself is small, but the first two were, but it is difficult to overcome. To solve the "24V DC Cooling Fan", we can try to use larger size fan. Should be in the same amount of wind, the big fan operating noise at low speed is less than the work of a small fan noise at high speed. Another factor is that we tend to ignore the fan bearings. Because "24V DC Cooling Fan" To friction between the shaft and the bearing rotates at high speed collision, it is also a major source of fan noise.