Allo Boss DAC + RPI Noisy when audio not playing

I have an Allo Boss DAC sitting on top of an RPI Zero-W. Power is supplied into the Boss’ via pin 1 & 14 on the J19 header from car battery after being passed through a 5V regulator circuit I pulled out out of a JBL Bookshelf Speaker system with one of those old and now-useless iPod connectors. The output of the Boss is fed into my factory Acura Bose Amplifier which then feeds the car speakers.

Naturally I’m using Volumio.

When my RPI is booting up after being powered on, I can hear all sorts of buzzing, popping and clicking noises from the output. It sounds like I can “hear” the RPI accessing files, turning on various services and doing what computers typically do during the boot process. Once I hear the “ready” tone and start playing an audio file the noise goes away to near silent and the music sounds epic.

5 seconds after pausing the song, the noisy RPI sounds return… and if I was listening at a rather high volume then that noise is truly awful. Resuming playback eliminates the noise.

Can anyone suggest a solution?

I have a DAC Boss and I plan to power it as this link says

https://www.allo.com/sparky-eu/boss-dac.html#downloads

Can you comment exactly how you power it?