  Resistance noise spectroscopy is applied to bulk single crystals of the
quasi-two-dimensional organic Mott insulator
$\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Cl both under moderate pressure and at
ambient-pressure conditions. When pressurized, the system can be shifted to the
inhomogeneous coexistence region of antiferromagnetic insulating and
superconducting phases, where percolation effects dominate the electronic
fluctuations [J. M\"uller {\it et al.}, Phys. Rev. Lett. {\bf 102}, 047004
(2009)]. Independent of the pressure conditions, at higher temperatures we
observe generic $1/f^\alpha$-type spectra. The magnitude of the electronic
noise is extremely enhanced compared to typical values of homogeneous
semiconductors or metals. This indicates that a highly inhomogeneous current
distribution may be an intrinsic property of organic charge-transfer salts. The
temperature dependence of the nearly $1/f$ spectra can be very well described
by a generalized random fluctuation model [Dutta, Dimon, and Horn, Phys. Rev.\
Lett. {\bf 43}, 646 (1979)]. We find that the number of fluctuators and/or
their coupling to the electrical resistance depends on the temperature, which
possibly relates to the electronic scattering mechanisms determining the
electrical resistance. The phenomenological model explains a pronounced peak
structure in the low-frequency noise at around 100 K, which is not observed in
the resistivity itself, in terms of the thermally-activated conformational
degrees of freedom of the ET molecules' ethylene endgroups.
