Idea to resolve 'pop' at the start and end of playback
The device has a pop at the start and end of playback. When viewing with a scope, I can see that the Rx pin is LOW normally; then switches to HIGH for playback; with modulation on top of the high state. It then writes it back to LOW when playback finishes. This transition causes the POP. I think if you write the pin HIGH and never let it go LOW again, the pop will go away.