The first stages of bearing defects will produce telltale non-synchronous vibration frequencies called "bearing tones" and their harmonics. Bearing tones at 0.006 inches per second peak (81 VdB) or higher are considered significant. Sometimes a new bearing will produce bearing tones, possibly because of damage during installation, shipping, or defective manufacture.
If the bearing defect is very small in size, such as a crack in one of the races, the vibration signature will show harmonics of the bearing tone with little or no fundamental frequency present. If the defect begins as a spall over a larger area of the race, the bearing tone fundamental will usually be higher in level than the harmonics. As the defect becomes worse, the overall level of the bearing tones will increase, as will the overall broadband noise level.