I've been able to get this same issue when I am laying in bed and lay on my side where my APP rub against the pillow. I've been able to reliably make the screeching sound by putting one airpod in my hand and tumbling it around or opening and closing my hands.

I still love my APP3, and still have my APP2, but have not made a change back to them. I think they feel so much better in my hear with the new tips, and sound way better.