Why does the Xiaomi Massage Gun 2 have different noises when used?

If the Xiaomi Massage Gun 2 has different noises, please refer to the following details:
1. Make sure the massage head is properly installed. If it is not properly installed, it will cause increased noise during use;

Note:
The red line in the figure is the schematic line for installation, while it is a glossy surface on the actual product.
2. Do not use the massage gun on areas with protruding bones or weak muscles. Please use this product on soft tissues with thick muscles. In order to protect the human body, the massage head adopts an internal hollow structure design. If it is accidentally hit on the protruding bone, it will produce a loud noise;
3. During use, the noise level will vary with the massage level and massage force, which is normal;
4. Different massage heads have different massage parts and functions, and all designed structural dimensions and weights are different, which will also produce different noises.