No sound on laptop after linux-libre 5.15

[Paxton Evans]

I've been encountering a strange sound issue lately, or rather, no sound
at all since  upgrading to linux-libre 5.15. The sound devices still
appear in alsamixer and Pavucontrol, but try as I might, there's just no
way to get them to play anything even though everything appears unmuted
and detected.

Rolling back to linux-libre 5.14.21 (guix
ea7233befb9570cce47e5ca71725b285a580cd22) totally fixes this issue. 

Troubleshooting sound issues on GNU/Linux is such a nightmare that I'm
hoping this list can help me, as I don't really know much about how
sound on our favorite OS really works, and don't have enough information
to file a bug. Can anyone give me pointers on where to start looking?
dmesg on 5.15.6 didn't seem to report anything strange.

I'm using a (Librebooted) MacBook 2,1 with no extra ("nonguix") channels
configured.

Thanks,
Paxton