Since none of the experts have chipped in, I'll hazard a guess.
The engines on all the A320 family produce a buzzsaw noise at takeoff power. Perhaps this is more noticeable on the A319 due to the shorter fuselage not absorbing as much of the vibrations.
I've not ridden a 321 yet, but if my 'theory' is correct they should be quieter than the 320s.
I assume they all come with the dog that barks during taxi
