Short wavelength density fluctuations of hydrated multilamellar phospholipid bilayers have been studied by molecular dynamics simulations in both the gel and liquid crystalline phases, and the results compared to recent inelastic x-ray scattering data [Phys. Rev. Lett. 86, 740 (2001)]. We confirm the existence of a highly dispersive sound mode, whose frequency and damping depend on the lipid phase, that the scattering arises mainly from in-plane motion of hydrocarbon chains, and we also identify a nondispersive mode attributed to motions of the chain terminal carbons.