Update 09.10.21: Meanwhile I hear this crackling also in Manjaro. However, I could now narrow it down: it definitely only comes from the left satellite box (2.1 system). Possibly a hardware error. I will soon connect other speakers for testing. If it doesn’t occur there anymore, it can only be the sound chip onboard. I have checked all cable connections, fits.
Perhaps this help
https://askubuntu.com/questions/1230833/annoying-click-popping-sound-on-ubuntu-20-04
or this
I found this and it works for me, BUT the change in
/sys/modules/snd_hda_intel/parameters/power_save
from 1 to 0 does not survive the reboot. Not even if I change
/etc/modprobe.d/audio_disable_power_save.conf
with the content
options snd_hda_intel power_save=0
After the reboot power_save is set to 1 again.
At least I can now rule out a hardware defect. I am seriously considering ümgehen the ALC887 …