  We have studied preheating of field perturbations in a 3-dimensional lattice
including the effect of scalar metric perturbations, in two generic models of
inflation: chaotic inflation with a quartic potential, and standard hybrid
inflation. We have prepared the initial state for the classical evolution of
the system with vanishing vector and tensor metric perturbations, consistent
with the constraint equations, the energy and momentum constraints. The
non-linear evolution inevitably generates vector and tensor modes, and this
reflects on how well the constraint equations are fulfilled during the
evolution. The induced preheating of the scalar metric perturbations is not
large enough to backreact onto the fields, but it could affect the evolution of
vector and tensor modes. This is the case in hybrid inflation for some values
of the coupling $g$ and the height of potential $V_0^{1/4}$. For example with
$V_0^{1/4} \simeq 10^{15}$ GeV, preheating of scalar perturbations is such that
their source term in the evolution equation of tensor and vector becomes
comparable to that of the field anisotropic stress.
