[PROBLEM] Smsl D300 Dac - loud "pop" noise before playing the first song

[DRONE7]

Not sure this will have the desired effect though there is some discussion and may be worth trying.
ALSA Power Management (DAPM) mutes and un-mutes for power-saving( generally for battery powered devices)

The 5 seconds delay before mute is turned on comes from the DAPM pmdown time. Main reason for this delay is to avoid clicks when a device is closed and then shortly after that opened again.

one suggestion is to create a file called snd_soc_core.conf in /etc/modprobe.d with this line in it:

Code:

options snd_soc_core pmdown_time -1

This disables DAPM 
You could try  and report results.

An alternative suggestion is to create a file /etc/modprobe.d/pmdowntime.conf with the following content

Code:

options snd_soc_core pmdown_time=600000

This increases the time between muting events