My son has a very noisy little female pekin and her sister who is almost always silent. We received two rehomed pekins two months ago that fitted right in with my son's flock and are virtually silent.
However, last year, when my son's drake came over to join my flock for a while (he was refusing to accept a muscovy female into the flock) the virtually silent sister became vocal and took over leadership of the flock of pekins plus one muscovy.
It is clear to us that with one very noisy little duck, the others have no need to be vocal, unless there is a particular need. Our particular need was for flock leadership. Drake is now back and the silent sister has become silent again. I feel sure if the very noisy little duck were to come to me for a week, the silent one would find her voice again!