I not sure exactly what is going on with your son but I thought I should share that my DS6 never had these type of behaviors until he started school. Now he does a lot more silly talk and a lot more screaming when he doesn't get his own way than he did when he was a toddler. He also started with a wierd arm motion that we had never seen before this year. These behaviors were mostly seen when he was around his peers and not when just one on one with adults.
Like you, we were very concerned that there was something else going on with him. DS6 was evaluated by a neuropsychologist last week and we were told that he does not have any diagnoses besides some mild anxiety to go along with his PGness. Most of these quirks are just that quirks. There is also some aschychrony at work and he is truly just trying to cope with the world around him.
My DS6's behaviors were worse when he started school, perhaps your son's behaviors will be lessened with the start of school.
