What is the reason for the electric fan to turn on the ZiZi ringing sound?

The electric fan a turn on the ZiZi ringing is the electric fan lack of oil or fan blade loose. First, lubricate the bearing 1, first disconnect the power supply, open the cover, remove the fan. 2, and then the fan blades, the motor part of the clean. 3, and then open the fan bearings, fan bearings inside and outside the wipe, plus the oil can be (Note: Do not use cooking oil to replace, because its particles are large, easy to bearings damage). Second, the fixed fan blade only need to remove the fan, the screw button tight, so that after firmly fixed, it will not vibrate to produce noise.