Ahh, ok.
I thought you meant that when he was really stressed he vocalized or rocked or tapped or something like that. A self-stimulatory behaviour or stereotypy. My son on autism spectrum used to have some of those behaviours when young but he also had a movement disorder so it was sometimes difficult to tell one from the other. My son used to get stressed very easily with tiny little changes in routine or other changes in the environment even. He still does actually and he's 24 LOL ~ If someone is 5 minutes late it's just so terrible.

I hope the tests all go well. He sure has a lot on his plate your little guy. You take care of yourself too. It'd be really good to get to the OT. He/she may have some ideas to help him and some advice for you.