Hello,
I would try these: but keep in mind the simplest is probably gonna be the one that works 🤦‍♀️
1. Hearing Test - Dr, school, hospital
2. Super sensitive hearing? What's humming in the house/environment when it happens? Try to source out the trigger.
3. Approach him differently- wake him up to a good morning song
4. JOIN him (if you haven't already) but take it on as over dramatic - maybe he will laugh instead
5. Start singing musicals loud & proud. They promote feelings & goose bumps depending on the notes.
6. Start counting while holding up your fingers one by one so he can watch & hopefully de-escalate. I do this to all my kids to "are you sleeping brother john".
7. Tell him what he's feeling & be simple stupid like you're 5
8. Music - playing piano
9. Art & sensory play - anything goes
10. Solid routine of his choosing

He knows he's getting something out of what he is doing. Negative or positive, he has your attention! And you are trying your best! Offer him choices for everything too 👍

He is better, still doing it but less than before. I think it is a combination of sensory issues and anxieties. I ended up buying some earplugs called calmer by flare to dampen the screeching which seem to help with my stress levels. Also I found ignoring it made him less likely to do it.
I hope it gets better for you soon

My son has gone through several phases 😩repetitive behavior that were at times unhealthy ,they all stopped when I ignored it and gave it no attention, In saying this it was not easy or will it be .i did a lot of crying in the bathroom and walks outside but it will stop and you will make it through . Also giving him other forms of outlet and forms of communicating /expression helps

They had done blood and a scan of his tummy. Nothing abnormal they said.

What has his Pediatrician done for workups?