Duct and "Micro Cooling Fan" in the face of the housing to be smooth seams, avoid rough, causing tearing sound. Duct and fan casing inner surface seams should be smooth, avoid rough, causing tearing sound. And because the "Micro Cooling Fan" will produce a series of pipeline resonance, small voice becomes so large, resulting in more noise. And because successive pipeline will resonate, make small voice becomes large, resulting in more noise. At design time, you can sometimes prevent sound material covered in duct outside noise can be reduced. "Micro Cooling Fan" in design, it is sometimes possible to prevent outside covered in duct sound material, can reduce noise.