Tiny Cooling Fan fan "eccentric"

"Tiny Cooling Fan" blades "eccentric": high-quality fan blades in its center of gravity on the axis, when the operation is very smooth, low noise, and low-quality fans, there will be some deviation, the center of gravity blades did not result in "eccentric" in the axis, so that "Tiny Cooling Fan" after turning up to the equivalent of a single oscillator (oscillator is on the motor shaft plus an eccentric), with the use of time longer, fan bearing gradually wear, or fan heat sink not securely installed, loose, etc., will cause increased noise vibration increases. Also may be because "Tiny Cooling Fan" of poor quality, poor lubrication, just start turn very astringent, and so turn to live, which was softened lubricants, small voice.