This makes a lot of sense but I got to thinking the one duck who I am almost positive is a boy kinda does that. This is not the one that vibrates. He will stick his bill in my hand and wiggle it around like he is looking for food and then he rubs up my arm and if I pick him up he wants to put his head over my shoulder or stand on top of my shoulder. Is this what ya'll are talking about?
The other duck that does vibrate I think is a girl cause she sure does quack a lot but she doesn't do this kind of behavior. When I realized it and put my hand to her chest she was just standing there. Does this mean that she is just getting the hang of it and will start soon? I assume females can be the more dominant duck over the male, yes?
I know if they get seperated she sure has near a heart attack trying to get to him. Just a flopping and quacking and he walks around frantically with his head high making small sounds.
Thanks you all for all your replies. Lots of my worries have eased. I would never had known that was what it was.