Ah! Thanks for mentioning the power-saving option. I'll research and test it out.
The 'unpredictable' timing may indeed be 5 seconds. It happens just after sound plays, or when I'm mucking with settings ... but never really when there is other sound coming out.
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Yep, you're right. Click comes from power-down on the sound card (
http://wiki.archlinux.org/index.php/ALSA). The test is to check out the module's power_save parameter. Anything > 0 means power saving is enabled.
cat /sys/module/snd_hda_intel/parameters/power_save
Inevitably, mine showed 5 (enabled). To disable it, I've:
sudo modprobe -r snd-hda-intel
sudo modprobe -i snd-hda-intel power_save=0
This has to be run each session, so I'll put it in bootlocal. Thanks for the direction.
Call that one closed.