  Interaction between the lattice and the orbital degrees of freedom not only
makes rare-earth nickelates unusually "bad metal", but also introduces a
temperature driven insulator-metal phase transition. Here we investigate this
insulator-metal phase transition in thin films of $\mathrm{SmNiO_3}$ using the
slow time dependent fluctuations (noise) in resistivity. The normalized
magnitude of noise is found to be extremely large, being nearly eight orders of
magnitude higher than thin films of common disordered metallic systems, and
indicates electrical conduction via classical percolation in a spatially
inhomogeneous medium. The higher order statistics of the fluctuations indicate
a strong non-Gaussian component of noise close to the transition, attributing
the inhomogeneity to co-existence of the metallic and insulating phases. Our
experiment offers a new insight on the impact of lattice-orbital coupling on
the microscopic mechanism of electron transport in the rare-earth nickelates.
