Last night I kept being woken up by a high pitched hissing/screeching sound.
Turns out it was coming from my phone. It stops when I touch the area around the power and volume buttons, though on a couple of occasions that’s actually made it much louder.
I saw one other post about this, with a suggestion that it could be Google voice assist, but my phone is fully de-Googled, with e/OS. Any suggestions?