  The scalar wave equation is considered in the background of a charged Vaidya
metric in double null coordinates $(u,v)$ describing a non-stationary charged
black hole with varying mass $m(v)$ and charge $q(v)$. The resulting
time-dependent quasinormal modes are presented and analyzed. We show, in
particular, that it is possible to identify some signatures in the quasinormal
frequencies from the creation of a naked singularity.
