- Electric field measurements from a single spacecraft have been used to study ion-sound turbulence observed within the transition region of a supercritical, quasiperpendicular shock. It is shown that the ion-sound waves observed upstream of the ramp are convected towards the ramp by the solar wind flow. The observed frequency of the ion-sound waves can be both lower and higher than the local electron cyclotron frequency depending upon the direction of wave propagation in the plasma rest frame. The ion-sound waves observed upstream of the ramp can not be generated either by an instability related to the gradient in the electron temperature or an electric current within the ramp. A comparison of wave vectors for distinctive wave packets indicate that non-stationary, short scale current layers formed in the processes of the ramp evolution might be the source of the free energy for such waves.