One idea. Asperger's / high function autism can run with Tourette's. I have a physician colleague who has this and is easily managed by a specific medication. Best wishes.
Possibilities are. Compulsion, vocal tic or stereotypy, that probably increases when he's anxious. Usually it can be treated with Clonidine or long-acting guanfacine, but it sometimes requires neuroleptics. If his cognitive ability is in the "average" range or above & his receptive & expressive language abilities are adequate, cognitive-behavioral therapy or specific habit-reversal therapy may help.