  We present a microscopic theory of cross-correlated noise processes, starting
from a Hamiltonian system-reservoir description. In the proposed model, the
system is nonlinearly coupled to a reservoir composed of harmonic oscillators,
which in turn is driven by an external fluctuating force. We show that the
resultant Langevin equation derived from the composite system
(system+reservoir+external modulation) contains the essential features of
cross-correlated noise processes.
