OK, question: most of my time was in military heavies and in those, the idea that you could hear someone tapping on a door in flight is a non-starter. Are A320s that much quieter? I just wonder if the CVR could really pick the sound up.
I seem to remember on UAL93 the sound of the attempts by persons external to the hijacked FD could be heard distinctly on the CVR, and that was a Boeing.