I haven't had a vibrating stomach. truth be told I've never really has anxiety/stress cause gastro issues other than diarrhea. i get occasional heartburn and bloating but all i have to look to there is what i've eaten.
i have had muscles in my abdomen twitch. i've had pretty much every muscle known on my body twitch. i've even vibrated and buzzed in various places.
in all mt years i've never even thought i could have parkinsons.