I tested the 5v pad and it was running about 2v, so I bridged it. Audio cleaned right up.
however
The solder bridge between the two gets extremely hot, to a concerning level. Not sure what’s up.
EDIT: so uh, I was wrong
I unsoldered the bridge and tried it again, but this time the audio was fine? I guess the original battery+ pad wasn’t soldered correctly and the board wasn’t getting enough power. Or something.