A theoretical and experimental investigation of quasi-harmonic friction-induced vibration is reported. The vibration is of near-sinusoidal form and is solely governed by dynamic friction forces. However, the friction-velocity curve must be of a particular shape for the vibration to occur. The amplitude of the quasi-harmonic vibration is shown to increase with sliding velocity until oscillation ceases at some upper velocity boundary. The introduction of suitable damping will quench the vibration entirely. The vibration can exist at high sliding velocities and as a consequence may influence the operation of automatic transmissions, brakes, and clutches.