I'm also affected by the issue, bought it in a local shop and they send it to their repair center where they couldn't reproduce it. As I got them back the issue was gone but now after two weeks I'm having the issue with the other side.
Disabling features or rotating the ear piece 180° didn't fixed the issue.
So far I found a fix on my side, but this might not help everyone (Would be nice if you give a feedback if it helps you too):
On my side the issue seems to be moisture related, the issue occurs when I got out of the shower and later go for long walk (There's still some moisture within the ear). It seems that the moisture gets into the AirPods and causes this high pitched noise (or the electric reacts to it?)
Not using your AirPods for a longer time within the charging case don't fix the issue for me, as maybe the moisture can't dry in this closed and tiny space. I let the AirPods within the charging case but left the case open. After 1-2 hours the issue is gone and I can use the AirPods again.