This paper investigates a particular subset of nonlinear distortion found in many automotive loudspeakers. This distortion occurs when the frequency response transfer function of the loudspeaker varies as its diaphragm moves from rest position. Subjective listening tests were performed, and the distortion was proven to be audible on music selections, even with small movements of the diaphragm (less than 3.0 mm peak to peak). These subjective tests correlate strongly with measured data from the described test method. The significance to audio system performance is discussed.