Random white noise from iPhone 12 Mini speakers

Random white noise, untriggered by me. No apps open, no microphone access to anything, the phone suddenly starts producing white noise. Sometimes it starts in my pocket or I’ll hear it in the car glovebox, it’s loud if the volume is up.

The only way to stop it is to turn the phone off. I have a voice memo of the sound but not sure how to post it here.