  We have investigated current-current correlations in a cross-shaped conductor
made of graphene ribbons. We measured auto and cross correlations and compared
them with the theoretical predictions for ideal diffusive conductors. Our data
deviate from these predictions and agreement can be obtained only by adding
contributions from occupation-number noise in the central region connecting the
arms of the cross. Furthermore, we have determined Hanbury -- Brown and Twiss
(HBT) exchange correlations in this system. Contrary to expectations for a
cross-shaped diffusive system, we find finite HBT exchange effects due to the
occupation-number noise at the crossing. The strength of these HBT exchange
correlations is found to vary with gate voltage, and very a distinct HBT effect
with large fluctuations is observed near the Dirac point.
