  Conductance fluctuation is usually unavoidable in graphene nanoribbons (GNR)
due to the presence of disorder along its edges. By measuring the low-frequency
noise in GNR devices, we find that the conductance fluctuation is strongly
correlated with the density-of-states of GNR. In single-layer GNR, the
gate-dependence of noise shows peaks whose positions quantitatively match the
subband positions in the band structures of GNR. This correlation provides a
robust mechanism to electrically probe the band structure of GNR, especially
when the subband structures are smeared out in conductance measurement.
