Noise generated by car components is more noticeable today because cars have generally become quieter. In one case, the power steering units in some cars emitted perceptible and very annoying noise from the power steering unit. The nature of the noise and its exact source was not clear. Experiments conducted to pinpoint the noise source are discussed in this paper. The results suggest that vibration of the pinion seal is the most common noise source. Two types of elastomer materials used for pinion seals have been tested for noise at a range of temperatures, pressures, and shaft speeds. A new criterion is suggested for prediction of vibration occurrence in seals and other rubber frictional members. The paper summarizes the investigation of this noise, and concludes with measures to prevent it.Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998