Re: my son make faces
I'm wondering how old your son is too.
Are we talking three or four?
It may very well be nothing much (imaginary friend sort of thing).
I have though observed children (3-5) on the Spectrum that make faces when they are doing their own thing or when someone is speaking to them as if they are speaking to themselves.
I'd just chill out about it though. If he's of school age and no one's bugging him about it, it's not affecting his self esteem, then I wouldn't worry too much.