Identify the root cause of 'Squeaking' or acoustic noise in a wave spring assembly.

Noise in wave spring assemblies is usually caused by 'Stick-Slip' friction between the spring crests and the mating surfaces or between the spring $O.D.$ and the housing. This occurs when the spring is under-lubricated or when the surface finish of the housing is too rough ($R_a > 1.6 \mu m$). As the spring compresses, the waves must move slightly; if they stick and then suddenly slip, high-frequency vibrations are excited. The solution is applying a dry-film lubricant like $MoS_2$ or increasing the axial preload to prevent micro-movements.