Thanks for the thoughts.

I've got enough clutter around not to need to spend several hundred dollars for a test card.

I also have no idea how to compile a new kernel, but do know that my being asked that confirms someone goofed.

Anyway, maybe something else is afoot.  Some noodles, please let me know what you think:

For starters:  I've noticed that sox fails periodically.  I've got a couple of scripts that play a brief OGG system sound every half hour, one on the hour, one five minutes before, to pace my day.  Actually, the first is set for 3 seconds later than 00, to avoid conflicts.  A .timer triggers a .service, which runs a one-line shell script that calls play (a sox command). 

This works until it doesn't, whereupon there are error logs, as follows (others that differ are further down ...).  (What exactly starts tripping it up?):

Apr 27 19:00:03 greystone systemd[1]: Starting Play sounds | pomo-in.service...
Apr 27 19:00:03 greystone bash[31026]: DIRFILE is /srv/greystone-data/users/eric/data/computer/media/sounds/chirps-notes/service-login.oga.
Apr 27 19:00:03 greystone bash[31027]: ALSA lib pcm_dmix.c:1089:(snd_pcm_dmix_open) unable to open slave
Apr 27 19:00:03 greystone kernel: traps: play[31027] trap divide error ip:7ff27953a37a sp:7ffc76cb7fa0 error:0 in libsox_fmt_ao.so[7ff27953a000+1000]
Apr 27 19:00:03 greystone bash[31026]: /home/locsh/pomo-in.sh: line 38: 31027 Floating point exception(core dumped) play $DIR$FILE
Apr 27 19:00:03 greystone systemd[1]: pomo-in.service: Main process exited, code=exited, status=136/n/a
Apr 27 19:00:03 greystone systemd[1]: pomo-in.service: Failed with result 'exit-code'.

Perhaps these offer some clues.

Separately, xrandr-related message storms crop up (revise xorg.conf?):

Apr 27 19:00:35 greystone gsd-color[5002]: no xrandr-DVI-I-0 device found: Failed to find output xrandr-DVI-I-0

Another weird one (no such device exists):

Apr 27 19:15:32 greystone dbus-daemon[1033]: [system] Activating via systemd: service name='net.reactivated.Fprint' unit='fprintd.service' requested by ':1.88' (uid=1000 pid=4878 comm="/usr/bin/gnome-shell " label="unconfined")
Apr 27 19:15:33 greystone systemd[1]: Starting Fingerprint Authentication Daemon...
Apr 27 19:15:33 greystone dbus-daemon[1033]: [system] Successfully activated service 'net.reactivated.Fprint'
Apr 27 19:15:33 greystone systemd[1]: Started Fingerprint Authentication Daemon.

Then (who/what is doing this, and why?):

Apr 27 19:15:35 greystone gnome-shell[4878]: Window manager warning: Overwriting existing binding of keysym 31 with keysym 31 (keycode a).
Apr 27 19:15:35 greystone gnome-shell[4878]: Window manager warning: Overwriting existing binding of keysym 32 with keysym 32 (keycode b).
Apr 27 19:15:35 greystone gnome-shell[4878]: Window manager warning: Overwriting existing binding of keysym 33 with keysym 33 (keycode c).
Apr 27 19:15:35 greystone gnome-shell[4878]: Window manager warning: Overwriting existing binding of keysym 34 with keysym 34 (keycode d).
Apr 27 19:15:35 greystone gnome-shell[4878]: Window manager warning: Overwriting existing binding of keysym 35 with keysym 35 (keycode e).
Apr 27 19:15:35 greystone gnome-shell[4878]: Window manager warning: Overwriting existing binding of keysym 38 with keysym 38 (keycode 11).
Apr 27 19:15:35 greystone gnome-shell[4878]: Window manager warning: Overwriting existing binding of keysym 39 with keysym 39 (keycode 12).
Apr 27 19:15:35 greystone gnome-shell[4878]: Window manager warning: Overwriting existing binding of keysym 36 with keysym 36 (keycode f).
Apr 27 19:15:35 greystone gnome-shell[4878]: Window manager warning: Overwriting existing binding of keysym 37 with keysym 37 (keycode 10).

Then, lots of these, followed by iptables reporting a bunch of outbound UDP/443 drops (who's the second user?):

Apr 27 19:16:16 greystone rtkit-daemon[1645]: Supervising 5 threads of 3 processes of 2 users.

The pulseaudio storms follow this, which I really don't follow (a socket client?  Doing what?):

Apr 27 19:17:07 greystone pulseaudio[4650]: Created 15 "Native client (UNIX socket client)"

Then, a storm of samba login attempts for five minutes, God knows how or from where because this is walled off, e.g.,

Apr 27 17:49:00 greystone smbd[29697]: [2022/04/27 17:49:00.868861,  1, pid=29697] ../../lib/param/loadparm.c:1870(lpcfg_do_global_parameter)
Apr 27 17:49:00 greystone smbd[29697]: pam_unix(samba:session): session closed for user nobody

Then a sox crash:

Apr 27 18:55:00 greystone systemd[1]: Starting Play sounds | pomo-out.service...
Apr 27 18:55:00 greystone bash[30988]: ALSA lib pcm_dmix.c:1089:(snd_pcm_dmix_open) unable to open slave
Apr 27 18:55:00 greystone kernel: traps: play[30988] trap divide error ip:7f2bd05b737a sp:7ffd64efe500 error:0 in libsox_fmt_ao.so[7f2bd05b7000+1000]
Apr 27 18:55:00 greystone systemd[1]: Starting Process error reports when automatic reporting is enabled...
Apr 27 18:55:00 greystone bash[30987]: /home/locsh/pomo-out.sh: line 38: 30988 Floating point exception(core dumped) play $DIR$FILE
Apr 27 18:55:00 greystone systemd[1]: pomo-out.service: Main process exited, code=exited, status=136/n/a
Apr 27 18:55:00 greystone systemd[1]: pomo-out.service: Failed with result 'exit-code'.
Apr 27 18:55:00 greystone systemd[1]: Failed to start Play sounds | pomo-out.service.
Apr 27 18:55:00 greystone whoopsie-upload-all[30991]: /var/crash/_usr_bin_sox.0.crash already marked for upload, skipping
Apr 27 18:55:00 greystone whoopsie-upload-all[30991]: /var/crash/_usr_lib_vmware_bin_appLoader.0.crash already marked for upload, skipping
Apr 27 18:55:00 greystone whoopsie-upload-all[30991]: All reports processed
Apr 27 18:55:00 greystone systemd[1]: apport-autoreport.service: Succeeded.
Apr 27 18:55:00 greystone systemd[1]: Finished Process error reports when automatic reporting is enabled.
Apr 27 18:55:39 greystone rsyslogd[1199]: -- MARK --
Apr 27 18:57:22 greystone gnome-shell[4878]: cr_parser_new_from_buf: assertion 'a_buf && a_len' failed
Apr 27 18:57:22 greystone gnome-shell[4878]: cr_declaration_parse_list_from_buf: assertion 'parser' failed

Another sox crash, followed by an xrandr storm:

Apr 27 18:55:00 greystone systemd[1]: Starting Play sounds | pomo-out.service...
Apr 27 18:55:00 greystone bash[30988]: ALSA lib pcm_dmix.c:1089:(snd_pcm_dmix_open) unable to open slave
Apr 27 18:55:00 greystone kernel: traps: play[30988] trap divide error ip:7f2bd05b737a sp:7ffd64efe500 error:0 in libsox_fmt_ao.so[7f2bd05b7000+1000]
Apr 27 18:55:00 greystone systemd[1]: Starting Process error reports when automatic reporting is enabled...
Apr 27 18:55:00 greystone bash[30987]: /home/locsh/pomo-out.sh: line 38: 30988 Floating point exception(core dumped) play $DIR$FILE
Apr 27 18:55:00 greystone systemd[1]: pomo-out.service: Main process exited, code=exited, status=136/n/a
Apr 27 18:55:00 greystone systemd[1]: pomo-out.service: Failed with result 'exit-code'.
Apr 27 18:55:00 greystone systemd[1]: Failed to start Play sounds | pomo-out.service.
Apr 27 18:55:00 greystone whoopsie-upload-all[30991]: /var/crash/_usr_bin_sox.0.crash already marked for upload, skipping
Apr 27 18:55:00 greystone whoopsie-upload-all[30991]: /var/crash/_usr_lib_vmware_bin_appLoader.0.crash already marked for upload, skipping
Apr 27 18:55:00 greystone whoopsie-upload-all[30991]: All reports processed
Apr 27 18:55:00 greystone systemd[1]: apport-autoreport.service: Succeeded.
Apr 27 18:55:00 greystone systemd[1]: Finished Process error reports when automatic reporting is enabled.
Apr 27 18:55:39 greystone rsyslogd[1199]: -- MARK --
Apr 27 18:57:22 greystone gnome-shell[4878]: cr_parser_new_from_buf: assertion 'a_buf && a_len' failed
Apr 27 18:57:22 greystone gnome-shell[4878]: cr_declaration_parse_list_from_buf: assertion 'parser' failed

This is interesting:  Pulseaudio is sinking some kind of input and then immediately iptables drops outbound invalid tcp/443 packets:

Apr 27 21:12:27 greystone pulseaudio[4650]: Sink input 89: proplist[media.name]: (data) -> (data)
Apr 27 21:15:23 greystone kernel: [ipt-invalid-out DROP] IN= OUT=lan0 SRC=192.168.1.2 DST=69.147.88.8 LEN=40 TOS=0x00 PREC=0x20 TTL=64 ID=0 DF PROTO=TCP SPT=36194 DPT=443 WINDOW=0 RES=0x00 RST URGP=0 
Apr 27 21:15:41 greystone rsyslogd[1199]: -- MARK --
Apr 27 21:15:43 greystone kernel: [ipt-invalid-out DROP] IN= OUT=lan0 SRC=192.168.1.2 DST=69.147.88.8 LEN=40 TOS=0x00 PREC=0x20 TTL=64 ID=0 DF PROTO=TCP SPT=36196 DPT=443 WINDOW=0 RES=0x00 RST URGP=0 

Another sox crash:

Apr 27 21:25:00 greystone kernel: traps: play[46530] trap divide error ip:7f44b374637a sp:7ffe381abb20 error:0 in libsox_fmt_ao.so[7f44b3746000+1000]
Apr 27 21:25:00 greystone bash[46530]: ALSA lib pcm_dmix.c:1089:(snd_pcm_dmix_open) unable to open slave
Apr 27 21:25:00 greystone bash[46529]: /home/locsh/pomo-out.sh: line 38: 46530 Floating point exception(core dumped) play $DIR$FILE
Apr 27 21:25:00 greystone systemd[1]: pomo-out.service: Main process exited, code=exited, status=136/n/a

Then, why does fwupd run?:

Apr 27 21:26:58 greystone systemd[1]: Starting Refresh fwupd metadata and update motd...
Apr 27 21:26:58 greystone systemd[1]: fwupd-refresh.service: Main process exited, code=exited, status=1/FAILURE
Apr 27 21:26:58 greystone systemd[1]: fwupd-refresh.service: Failed with result 'exit-code'.
Apr 27 21:26:58 greystone systemd[1]: Failed to start Refresh fwupd metadata and update motd.

And, nvidia-modeset errors (why do these run if nvidia-modeset=0?) followed by an invalid outbound tcp/443 packet.  Very weird:

Apr 27 21:43:00 greystone kernel: nvidia-modeset: ERROR: GPU:0: Idling display engine timed out: 0x0000917d:0:0:1079
Apr 27 21:43:02 greystone kernel: nvidia-modeset: ERROR: GPU:0: Idling display engine timed out: 0x0000917c:0:0:1095
Apr 27 21:43:04 greystone kernel: nvidia-modeset: ERROR: GPU:0: Idling display engine timed out: 0x0000917c:1:0:1095
Apr 27 21:43:21 greystone kernel: [ipt-invalid-out DROP] IN= OUT=lan0 SRC=192.168.1.2 DST=204.237.133.116 LEN=40 TOS=0x00 PREC=0x20 TTL=64 ID=0 DF PROTO=TCP SPT=38970 DPT=443 WINDOW=0 RES=0x00 RST URGP=0