I get the audio crackle also, been trying to figure it out for a while. Some people seem to have solved it by disabling power saving on the audio card. Didn’t work for me but might work for you.
cat /sys/module/snd_hda_intel/parameters/powersave
If it returns a “1” then power save is active
i_am_not_a_robot@feddit.uk 38 minutes ago
I’ve not used paint.net so this might be completely off the mark, but Pinta is a good little paint program which might be a reasonable alternative.