A whine in the noise background of a coasting automobile presented a quality‐control problem to the manufacturer. The objectionable signal had the character of a sinusoidal sound whose frequency was velocity‐dependent and which faded in and out of the background noise as speed decreased from 70 to 20 mph. This whine was attributed to the differential gears. The analysis undertaken to determine the nature of the whine, its association with the differential gears, and the explanation for the details characterizing its occurrence are described. In addition, the design of an instrument to be used in the inspection line for detection of incipient noisy cars is presented. [Supported by American Motors Corporation, Kenosha, Wisconsin.]