D.R.
Hi J.,
Does he also get ear infections or fluid build up in his ears with colds? My son was a recreational screamer when he was that age. He had frequent ear infections and/or fluid and we discovered that he needed to get PE tubes in his ears.
The first time he started to scream after the tubes, he scared himself silly and it pretty much stopped.
If you've ruled that out, you could try locking eyeballs with him and giving him a firm 'No'.
Hope this helps