Thanks for the info and suggestion. I opened up and see the chip you’re likely referring to.
I can confirm there aren’t magnets nearby, as the machine is generally on my lap when it happens (nothing in pockets). Sometimes just lifting it off the table is enough. I was able to duplicate the behavior a few minutes ago by setting the laptop on a stone counter–no magnets anywhere nearby. Sounds a lot like a flaky connection or short circuit.
Not blaming FW for any of this–the machine’s been around awhile and not gently used.