Noise in a bearing is caused by a number of factors that increase vibration. Rough or damaged balls or raceways, poor ball/raceway roundness, contamination inside the bearing, inadequate lubrication, incorrect shaft or housing tolerances and incorrect radial play can all contribute to noise. A good quality, low noise bearing will have excellent surface finish on balls and raceways and the roundness of the balls and bearing rings will be very closely controlled. Specifying a radial play that allows the bearing to operate with almost zero radial play when in use will help to control noise. If the shaft or housing tolerances are incorrect, the bearing can be too tight leading to excessive noise while poor shaft or housing roundness can distort the bearing rings, also causing the bearings to be noisy. In a good quality bearing, a low noise lubricant is recommended as finely filtered greases will allow the bearing to run quietly due to the absence of larger solid particles. Poor fitting practices can cause dents in the bearing raceways which will greatly increase vibration. Finally, a low noise bearing must be free of contaminants so, if the bearing is not used in a very clean environment, protection against dirt, such as contact seals, should be considered.