  We present a theoretical study on the origin of some findings of recent
experiments on sonic analogs of gravitational black holes. We focus on the
realization of a black-hole lasing configuration, where the conclusive
identification of stimulated Hawking radiation requires dealing with the
implications of the nonstationary character of the setup. To isolate the basic
mechanisms responsible for the observed behavior, we use a toy model where
nonstationarity can be described in terms of departures from adiabaticity. Our
approach allows studying which aspects of the characterization of black-hole
lasing in static models are still present in a dynamical scenario. In
particular, variations in the role of the dynamical instabilities can be
traced. Arguments to conjecture the twofold origin of the detected
amplification of sound are given: the differential effect of the instabilities
on the mean field and on the quantum fluctuations gives some clues to separate
a deterministic component from self-amplified Hawking radiation. The role of
classical noise, present in the experimental setup, is also tackled: we discuss
the emergence of differences with the effect of quantum fluctuations when
various unstable modes are relevant to the dynamics.

Quantum Gases