One of the unique features of Dirac Fermions is pseudodiffusive transport by evanescent modes at low Fermi energies when disorder is low. At higher Fermi energies, i.e., charge carrier densities, the electrical transport is diffusive in nature and the propagation occurs via plane waves. In this study, we report the detection of such evanescent modes in the surface states of topological insulator through 1/f noise for the first time. While signatures of pseudodiffusive transport have been seen experimentally in graphene, such behavior is yet to be observed explicitly in any other system with a Dirac dispersion. To probe this, we have studied 1/f noise in topological insulators as a function of gate voltage, and temperature. Our results show a nonmonotonic behavior in 1/f noise as the gate voltage is varied, suggesting a crossover from pseudodiffusive to diffusive transport regime in mesoscopic topological insulators. The temperature dependence of noise points towards conductance fluctuations from quantum interference as the dominant source of the noise in these samples.