  We present simulation results of the (2+1)d four-fermion model with a baryon
chemical potential. We examine temporal correlation functions of the vector
meson, and find evidence of phonon-like behavior characterised by a linear
dispersion relation in the long wavelength limit. We also discuss the
consistency of our numerical results with analytical solutions to the Boltzmann
equation corresponding to zero sound. We argue that our results provide the
first evidence for a collective excitation in a lattice simulation.
