  We calculate the disconnected contribution to the form factor for the
semileptonic decay of a D-meson into a final state, containing a flavor singlet
eta meson. We use QCDSF n_f=2+1 configurations at the flavor symmetric point
m_u=m_d=m_s and the partially quenched approximation for the relativistic charm
quark. Several acceleration and noise reduction techniques for the stochastic
estimation of the disconnected loop are tested.
