What causes the noise of micro reduction motors?

Micro reduction motors are generally made by professional manufacturers and then sold after assembly. Although the design of micro reduction motors is simple, it has a role that cannot be ignored. It is also called a gear reducer. However, noise occasionally occurs in daily use and work, so how do we solve it?
1. Gear accuracy: Is the gear accuracy and fit of the DC planetary reduction motor ok?
3. Is the motor itself noisy: high-precision motors have low noise, some imported motors have very low noise, and poor quality motors have high noise.
2. Gear lubricant: Is there too much oil? If too much oil is added, there will be no problem when the DC planetary reduction motor gearbox is just started, but after a long time, it will cause the gears to slip; of course, there will be a gap;
4. Is the installation reasonable:
The standard DC planetary reduction motor gearbox generally has the first layer of gears made of plastic and the rest are steel parts, and the second layer is all steel parts. The first layer of gears determines the size of the noise, so when choosing a gearbox, if there is a requirement for noise, then the first layer must be designed as plastic