The problem started today. I wanted to watch a video with firefox and the sound was vibrating. As if it was saturating, even though it wasn't very loud.
I started fiddling. I tested with VLC and the sound was OK. I removed-purged firefox. Still vibrating. I removed-purged pulseaudio and rebooted.
Vibrating sound in firefox and NO sound at all with VLC. I tried a few other command line instructions found online and rebooted. Now I have no
sound at all, even in firefox.

Now I'm afraid to do anything except sudo inxi -SMA, because when I fiddle I make things worse. I should have left things alone (I could always
download my video to watch it). sudo inxi -SMA says:

Host: lub Kernel: 5.15.0-56-generic x86_64 bits: 64
Desktop: LXQt 0.14.1 Distro: Ubuntu 20.04.5 LTS (Focal Fossa)
Type: Laptop System: Acer product: Aspire 7739ZG v: V1.04
serial: LXRUM02001148018E07200
Mobo: Acer model: HMA71_CP v: Type2 - Board Version
serial: Type2 - Board Serial Number BIOS: Insyde v: 1.04
date: 10/11/2011
Device-1: Intel 5 Series/3400 Series High Definition Audio
driver: snd_hda_intel
Device-2: NVIDIA GF108 High Definition Audio
driver: snd_hda_intel
Sound Server: ALSA v: k5.15.0-56-generic