You wouldn't be using a PRNG for this, because what would be the point? The idea would be to generate some plausible-sounding audio, not garbage that a listener would obviously know isn't real.

Really, though, in general there's just no point to this altogether; just cutting power/data to the mic is fine. There's no need to attempt to fool someone with fake audio, outside of some very edge-case scenarios that I'm sure Dell (rightly) does not care about.