  We present systematic temperature-dependent resistance noise measurements on
a series of ferromagnetic Ga$_{1-x}$Mn$_{x}$As epitaxial thin films covering a
large parameter space in terms of the Mn content $x$ and other variations
regarding sample fabrication. We infer that the electronic noise is dominated
by switching processes related to impurities in the entire temperature range.
While metallic compounds with $x>2$ % do not exhibit any significant change in
the low-frequency resistance noise around the Curie temperature $T_\mathrm{C}$,
we find indications for an electronic phase separation in films with $x<2$ % in
the vicinity of $T_\mathrm{C}$, manifesting itself in a maximum in the noise
power spectral density. These results are compared with noise measurements on
an insulating Ga$_{1-x}$Mn$_{x}$P reference sample, for which the evidence for
an electronic phase separation is even stronger and a possible percolation of
bound magnetic polarons is discussed. Another aspect addressed in this work is
the effect of ion-irradiation induced disorder on the electronic properties of
Ga$_{1-x}$Mn$_{x}$As films and, in particular, whether any electronic
inhomogeneities can be observed in this case. Finally, we put our findings into
the context of the ongoing debate on the electronic structure and the
development of spontaneous magnetization in these materials.
