  We propose a simple discrete model to study the nonequilibrium fluctuations
of two locally coupled 1+1 dimensional systems (interfaces). Measuring
numerically the tilt-dependent velocity we construct a set of stochastic
continuum equations describing the fluctuations in the model
  The scaling predicted by the equations are studied analytically using dynamic
renormalization group and compared with simulation results. When the coupling
is symmetric, the well known KPZ exponents are recovered. If one of the systems
is fluctuating independently, an increase in the roughness exponent is observed
for the other one.
