I have done nothing (just mail), but sound is working again. I just opened a new youtube tab and video, and it worked. And speaker-test confirms. I go back to the video I tested this morning, and it also works. So does VLC. Baffling. as to the kernel, looking on my logs: 2021-04-18 00:20:40+02:00 - Booting the system now === Linux Telcontar 5.3.18-lp152.69-preempt #1 SMP PREEMPT Tue Apr 6 11:41:13 UTC 2021 (d532e33) x86_64 x86_64 x86_64 GNU/Linux 2021-04-19 23:45:15+02:00 - Booting the system now === Linux Telcontar 5.3.18-lp152.72-preempt #1 SMP PREEMPT Wed Apr 14 10:13:15 UTC 2021 (013936d ) x86_64 x86_64 x86_64 GNU/Linux 2021-04-27 08:43:52+02:00 - Booting the system now === Linux Telcontar 5.3.18-lp152.72-preempt #1 SMP PREEMPT Wed Apr 14 10:13:15 UTC 2021 (013936d ) x86_64 x86_64 x86_64 GNU/Linux So, kernel did not change on the 27th, it changed on the 19. But on the 19 I had no sound problem.