  We have studied low frequency resistance fluctuations (noise) in a single
crystal of the rare earth perovskite manganite Pr$_{0.63}$Ca$_{0.37}$MnO$_3$
which shows a charge ordering transition at a temperature $T_{CO}$ ~ 245K. The
noise measurements were made using an ac bias with and without a dc bias
current imposed on it. We find that the spectral power $S_V(f)$ contains two
components - one broad band 1/f part that exists for all frequency and
temperature ranges and a single frequency Lorentzian of frequency $f_c$ which
is strongly temperature dependent. The Lorentzian in $S_V(f)$ which appears due
to Random telegraphic noise (RTN) as seen in the time series of the
fluctuation, is seen in a very narrow temperature window around $T_{CO}$ where
it makes the dominating contribution to the fluctuation. When the applied dc
bias is increased beyond a certain threshold current density $J_{th}$, the
electrical conduction becomes non-linear and one sees appearance of a
significant Lorentzian contribution in the spectral power due to RTN. We
explain the appearance of the RTN as due to coexisting Charge ordered (CO) and
reverse orbitally ordered (ROO) phases which are in dynamical equilibrium over
a mesoscopic length scale ($\approx 30nm$) and the kinetics being controlled by
an activation barrier $E_{a} ~ 0.45eV. The 1/f noise is low for $T>>T_{CO}$ but
increases by nearly two orders in a narrow temperature range as $T_{CO}$ is
approached from above and the probability distribution function (PDF) deviates
strongly from a Gaussian. We explain this behavior as due to approach of charge
localization with correlated fluctuators which make the PDF non-Gaussian.
