I've never taken abilify or risperadol myself for tics... i tend to stick with the benzo's... but i can say from experience that when i hit my teen years my tics also got worse, especially my vocals... but mine were more high pitched whinning and screeching than grunting (so high pitched it sometimes annoyed the dog)... and holidays were always a big stresser for me as well.

It could be the increase in tics has nothing to do with the meds at all, and is purely environmental... does he maybe have a big project, or a dance, or maybe he's worried about a bully at school, or a girl... i remember middle school/high school all too well and there are so many little things that would stress me out to the max....

at 13 he might not want to tell his mum whats on his mind, but it might be good to just remind him of any calming techniques u have... breathing, relaxing, video games etc... that he can turn to when things are getting to stressful for him....

anyway, just a thought.