Duck vibrates head and then nips at me?

[sowNreap]

I have had my ducks vibrate their necks at me before. I feel like it means they are overstimulated and want me to stop something. It always happened when I touched them, which I don't do anymore and they no longer vibrate at me. They still like me, run to greet me, hang out with me, ect.

Same with me. One of my drakes vibrated his neck while feeding treats but I tried to pet him while doing so. I stopped trying to pet him & he stopped vibrating.