Does sound very odd. I have to ask did you (and others) have headphones in by any chance?
In response to the comment about short platforms. The automated system announces passengers to move forward, the guard should be making principal announcements and you’ve also got Station CIS screens and audio...
LOL reminds me of the time I was on an 8 car 350 en route to Crewe, the announcements were made and were crystal clear about short platforms at Atherstone, we pulled into the station and a bloke with headphones appeared at a set of doors in the rear set and therefore couldn’t allight, I remember him pelting through the train towards the front set, don’t know if he made it in time though.
I do agreee that one some trains the tannoy is poor though, in another incident I was on a EMT dmu in the summer, Liverpool to Manchester,I think it was the Norwich train possibly a 156 or 158. 4 car.
We stopped in the platform at Hunts Cross, obviously knew something was wrong as we weren't booked to call there, an announcement was made but was inaudible.
In the end the TM walked through the train advising everyone that there was a bridge strike near Widnes so she obviously knew about the tannoy, unless a fellow pax reported it.
Moved slowly forward to Widnes were we sat for a while, called at Warrington. Train was FAS from there. 29 late into Piccadilly.