@meowski
The source of the banging was never conclusive and was heard subsequent to the implosion. Nobody in the sub banged on anything; it just went blooey in an instant.
@meowski
The implosion was deemed to have occurred on or near the time they lost communication with the vessel, so there was no deployment of search/rescue audio detection deployed at that instant. The assessment was made by the USCG which prompted SeaGate to issue the statement to that effect when it did.