Most of my stutters are like that. My jaw will lock and move up and down really fast like I'm freezing cold. while it happens it feels like I'm trying to push the word out. Other times on words with "ch" for example I'll kind of bite down on my teeth really hard while my jaw locks. I saw a speech therapist once that told me it's because at one point I found a way to sort of "hide" the vocalized stutter so it isn't as obvious but idk if that's the reason.