We describe recent results in an ongoing investigation of student understanding of sound, especially of sound propagation in solid media. We have recently administered written questions and conducted interviews to probe student reasoning about this topic, specifically the effect on the pitch or frequency of a sound that is propagated from one object to another. Our findings show that the concepts of propagation and resonance are not functionally distinguished by these students; many students seem to be distracted by the resonant properties of an object that is propagating sound. Furthermore, students have more difficulty when considering propagation of a sound through objects with sound generating properties than with objects not associated with sound generation. This work forms the basis for instructional materials to improve student learning, especially among preservice teachers. The curriculum developed to date is reasonably successful at addressing these student difficulties.