For some reason, that Chewbacca shouting at Han clip just made me cry laughing. Silly things like that do it sometimes. I can watch most comedy films from beginning to end and not even crack a smile, then something like this will set me off.
no, that audio was too clear. It wasn't coming from inside the helmet. It's the same voice that called action and even gave Prowse stage directions ("turn"). My bet is also on Marquand. Prowse is just miming the lines along to Richard. Probably because it was a long take and easier for Richard to read than for Prowse to memorize and to get the right pacing that Richard wanted.