In this sort of situation, I think it is a courtesy of the pilot to inform passengers, but there maybe all kinds of operational reasons why he didn't.
As you say, you all landed safely - yes, I'd point to the noise suppression system as the first culprit. The concept of the technology is to create alternative waves to cancel out those that a generated by the props. Not sure if we have any sound engineers here, but if that got out of synch, then suddenly 1-1=0 becomes 1+1=2.