Rayleigh surface wave velocities in Ag/Cr and Au/Cr metallic superlattices have been measured by Brillouin scattering spectroscopy. These metallic superlattices were prepared by the metal-MBE method. X-ray diffraction measurements indicated that the structures of Ag/Cr and Au/Cr superlattices were almost the same. In the Au/Cr superlattices a maximum in a plot of surface wave velocities as a function of the bilayer thickness was observed. On the contrary, a distinct dip was shown in Ag/Cr systems. This anomalous behavior of the sound velocity could not be attributed to the expansion and the contraction of the lattices. Differences in atomic scale structure in the interface seem to play a major role in these systems.