[en] If the low-temperature properties of glasses are determined by strongly interacting defects, then in a superconducting metallic glass the apparent density of two-level-system (TLS) glass should be greater in the superconducting than in the normal state. This difference affects the acoustic properties of the material. Published measurements of sound attenuation and velocity in Pd₃₀Zr₇₀ exhibit anomalies consistent with an increased density of TLS's in the superconducting state, but further experiments are needed to distinguish the effects caused by changes in the interactions between TLS's as opposed to changes in the coupling between each TLS and the conduction electrons