What are the reasons for the bearing ringing?

Update:2018-10-13

After a long-term summary by technicians, NTN tilting pad thrust bearing have the following 27 reasons, and there may be many that we have not encountered before, and will slowly make up later.
1. The NTN bearing is mixed with impurities such as sand or carbon particles to act as an abrasive;
2. The NTN bearing is mixed with moisture, acid or paint and other dirt, which acts as a corrosive effect;
3. The clearance of the NTN bearing is too small (the selection is not appropriate);
4. The type of lubricating oil or grease is incorrectly selected;
5. Insufficient lubrication (oil level is too low, oil or grease leaks through the seal);
6. The NTN bearing is flattened by the seat hole (the roundness of the seat hole is not good, or the seat hole is not twisted straight);
7. The horn of the bottom surface of the NTN bearing housing is not flat (resulting in deformation of the seat hole or even cracking of the NTN bearing housing);
8. There are debris in the hole of NTN bearing housing (residue of chips, dust particles, etc.);
9. The seal is eccentric (wearing adjacent parts and rubbing);
10. NTN bearings are subjected to additional loads (NTN bearings are axially tightened, or two fixed-end NTN bearings on one shaft);
11. The thermal elongation of the shaft is too large (NTN bearing is subjected to static and indeterminate axial additional load);
12. The clearance of the NTN bearing is too small, and the rotation is too tight (the tightening sleeve is too tight);