  The $f^{-\gamma}$ sloped current noise power spectra, observed in organic
semiconductors, have been interpreted within a {\em variable range hopping}
mechanism of the fluctuations. The relative current noise power spectral
density ${\cal S}(f)=S_I(f)/I^2$ exhibits a maximum at the {\em trap-filling
transition} between the {\em ohmic} and the {\em space-charge-limited-current}
regime [Phys. Rev. Lett., {\bf 95}, 236601, 2005]. Here, we discuss the
electronic conditions determining the crossover from ohmic to
space-charge-limited transport. These arguments shed further light on the need
to adopt a {\em percolative} fluctuation picture to account for the competition
between insulating and conductive phases coexisting at the {\em transition},
where small changes in the external bias lead to dramatic effects in the
fluctuations.
