I run Linux on my HNK Hades Canyon NUC.
(Fedora 28 with kernel 4.18-rc7)
There is a very subtle yet annoying audio POP that happens immediately before & after any normal audio play-back.
My intuition felt that issue resembled some kind of power-saving feature, and I was not wrong.
To solve this issue simply disable the power saving feature of the Intel HD Audio driver in Linux.
To observe the current values:
# cat /sys/module/snd_hda_intel/parameters/power_save
# cat /sys/module/snd_hda_intel/parameters/power_save_controller
The value of "1" for the power_save is the worst possible default imaginable, it's the most absurdly aggressive power saving mode possible. It would have been more sane to default to 10 or 20 seconds, but I digress.
The value of "Y" simply indicates the power saving feature is enabled.
To disable these features on a running system, simply use standard IO on the same files:
# echo 'N' > /sys/module/snd_hda_intel/parameters/power_save_controller
# echo '0' > /sys/module/snd_hda_intel/parameters/power_save
(Edit: made a copy/paste correction here to correctly show the stdio echo into the files)
Repeat the earlier steps to verify the change.
To make the change more permanent you can re-build your kernel with modified CONFIG_SND_HDA_POWER_SAVE_DEFAULT parameter, see the kconfig documentation for details.
Another option might be to blacklist the kernel module on bootup, or write a scrip to set these values on boot.
Anyways, hope this helps someone.
Btw, to make it permanent, the following works on fedora and others:
# echo `options snd-hda-intel power_save=0` > /etc/modprobe.d/alsa-base.conf
fixes not just pops but also constant "ground loop" kind of speaker humming noises
The best way to eliminate the ground-loop audio hum would be to use the toslink SPDI/F connector available on the Hades Canyon. However, I've had trouble getting that to function in upstream kernels (in the ALSA sub-system). If anybody solves that topic, please let me know.