I agree that his
pediatrician needs to see him & a video of an episode.
Learned behaviors typically start at 6 months, so he can have learned that his shriek gets instant attention, but you can't ignore it till you know he's ok. If ok, ignore it consistently till he gives it up. Intermittently reinforcing it makes it last longer. Attend to him while he's happy. with phrases like, " Up? You want up?" & a smile.