We had a somewhat similar concern with our 5 year old. We asked for a referral to a pediatric neurologist who examined her, and felt it was a tic-like thing she would outgrow. He added that if she didn't figure out how to control it, that a referral to a behavioral therapist would be in order. Interestingly, he added that something like 1 in 3 kids has some kind of "tic" if you look closely enough. As far as other kids noticing-so far only one girl said something and she called it "dancing," which was sweet.
Having said that, maybe keep a journal of how and when he does it then ask for some referrals from your pediatrician. Maybe a neurologist and or a child psychiatrist with experience in Tourette's. Feel free to email me.
J.