  We point out that the velocity of propagation of sound wavepackets in a
Bose-Einstein condensate filling a three-dimensional cubic optical lattice
undergoes a maximum with increasing lattice depth. For a realistic choice of
parameters, the maximum sound velocity in a lattice condensate can exceed the
sound velocity in a homogeneous condensate with the same average density by
30%. The maximum falls into the superfluid regime, and should be observable
under currently achievable laboratory conditions.
