  We present a model for the aperiodic variablity of accreting Black Hole
Candidates (BHC) along with model light curves. According to the model this
variability is the combined outcome of random (Poisson) injection of soft
photons near the center of an extended {\sl inhomogeneous} distribution of hot
electrons (similar to those advocated by the ADAF or ADIOS flows) and the
stochastic nature of Compton scattering which converts these soft photons into
the observed high energy radiation. Thus, the timing properties (PSD, lags,
coherence) of the BHC light curves reflect, to a large extent, the properties
of the scattering medium (which in this approximation acts as a combination of
a {\sl linear} amplifier/filter) and they can be used to probe its structure,
most notably the density profile of the scattering medium. The model accounts
well for the observed PSDs and lags and also the reduction in the RMS
variability and the increase in the characteristic PSD frequencies with
increasing source luminosity. The electron density profiles obtained to date
are consistent mainly with those of ADIOS but also with pure ADAF flows.
