Reason:
1. The layout of the cable in the chassis is unreasonable, and the computer fan encounters the cable when it is rotating, causing the problem of loud noise in the chassis;
2. The computer fan in the case is not firmly installed, and vibration occurs when the fan rotates, causing the case sound to suddenly become louder;
3. The chassis fan is dusty, and the resistance of the fan increases when the fan rotates, which will cause the computer fan to make a loud noise;

Solution:
Open the case to make the panel, remove the power supply, remove the front panel of the case, and use a vacuum cleaner to suck away the dust in the front panel, power supply, cpu radiator, and graphics card fan (if any). These places can hide dust most.
If you don't have a vacuum cleaner, you can blow these places with a pump. If you take it outside the house, you will get a lot of dust. Use a cloth dipped in alcohol to clean the inside of the case. If there is no alcohol, just use a little water to moisten the cloth. Let it dry in a ventilated place for 1 hour. If you wipe it with water in the previous step, it will take longer and let it cool for one day. Finally, install the power supply case.