interesting question. My pekins are loud mouths sometimes but not every day. my neighbors dont mind them, its the geese they dont appreciate so much.
The thought that first came to my mind was hoping for a quiet duck is like hoping for a dry water. or wet fire.
except muscovies. but they aren't really ducks are they?
on second thought, I have noticed my welsh harlequins are quieter than my other breeds. and my khaki campbell isnt too loud either. its somewhat subjective though - you might think something is loud that i consider quiet. and vice versa. sorry im not very much help. but its fun to think about.