In my experience:
Pekin's are very loud when they want to be though probably not as loud as a rooster they do call alot more frequently (especialy when food is around, or they see you, or there taking a bath or there......)
Runners are loud but not nearly as loud as Pekins though they seem to come to associate humans with food realy quickly and like to let you know there hungry (we had one female Runner for 2 weeks and she was ver talkative.)
Khaki Campbell's (though you were not asking about them) are fairly quiet, they do have a deep loud quack when they want to but seem to seldome use it and prefer to make reasonably quiet almost duckling like sounds (though there still deeper in voice and louder than Cayugas)
Cayugas are very very quiet though they still have a loud quack it is more on par with a wild mallard hen and generaly given a lot less frequently. When two females are "fighting" over a drake though they can be talkative but generaly they just make small almost duckling like noises even when your coming to give them food. Generaly the hens seem to be quieter than the drakes when there making these type of noises.
Muscovies are as everyone has said very quiet and you would not ever hear them unless you were basicaly standing beside them.
Hope that helps!