For me the greatest Quiet Coach annoyance is the continuous stream of PA announcements. Why cannot these be suppressed in these vehicles. Long lists of every little stop the service will make, repeated after every stop. Lengthy diatribes from the refreshment vehicle about what is on offer. Admonitions about where the emergency instructions can be found, remembering to take everything with you, be careful in case the platform is slippery, no luggage on seats, you can't use tickets of type X, Y or Z, make sure you have tied your shoelaces, yadda, yadda, yadda - all repeated after every stop.
Quiet means Quiet. Not just me being so.