Yes, the drake has a curled feather on his back like my avatar, Mucky. The females have a raspy quack and when they all sound off together, I like to say it sounds like a bunch of grandmas playing poker and one of them said something to make them all laugh. The drake has a soft voice like the trolling motor of a boat. Don't know if that's for all breeds but I think it's pretty common. If yours all look alike and some are laying eggs, I think they are all females. Especially if you have not noticed any mating behavior. Although my females will imitate mating with each other. So listen to see if any have a different voice and look for the curled tail. Males will also do a funny trumpet sound to kind of show off. They will puff up their heads and rear back and lift their chest out of the water making a sort of grunt.