  Fluctuation spectroscopy is used to investigate the organic
bandwidth-controlled Mott system $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Cl. We
find evidence for percolative-type superconductivity in the spatially
inhomogeneous coexistence region of antiferromagnetic insulating and
superconducting states which develops under pressure at low temperatures. When
the superconducting transition is driven by a magnetic field, percolation seems
to be dominated by unstable superconducting clusters upon approaching $T_c (B)$
from above, before a "classical" type of percolation is resumed at low fields,
dominated by the fractional change of superconducting clusters. The $1/f$ noise
is resolved into Lorentzian spectra in the crossover region where the action of
an individual mesoscopic fluctuator is enhanced.
