Did you manage to find solution?
I have the same problem with Orange PI PC, 3.5 output jack.
Reproduction:
In the fresh install of Buster server/4.19/2019-07-15, play any wav file with aplay.
There are no problems with sound playback on Xenial 3.4.
There are same problems with latest kernel (5.3)
There are two separate problems:
1) It tooks about 1.5 seconds for analog codec to wake from power down.
First 1.5 seconds of sound is not played, there is clicking sound instead.
There is a click after 5 seconds of playback (power down).
2) There are noticeable clicks at the start and stop of playback.
(1) can be solved with:
echo -1> /sys/devices/platform/soc/1c22c00.codec/cdc/pmdown_time
(thanks for sharing it!)
(2) is caused by audio driver which sets PWM output to zero while preparing playback and after playback.
It should let it running ar 50% ratio instead.
The only way to play click-free sounds messages OPI currently is using dmix:
https://forum.armbian.com/topic/1960-configuring-orange-pi-pc-for-analogue-line-out-jack-audio-output-and-simultaneous-hdmi-output-with-software-mixing/
and pushing silent data constantly, like some people did on rapsberry PI
before similar issue was fixed: https://github.com/raspberrypi/linux/issues/128
