I'm pretty sure this is the bug report! Theoretically, it should be fixed in SteamOS 3.5 https://steamcommunity.com/app/1675200/discussions/1/3472864793301381863/

Yup! It seems that switching the resolution is the key. For me, at least, the sound works fine on every other resolution switch. I usually switch it to something lower, then something else, then back to the resolution I want. It's pretty annoying, but it doesn't take too long and is way less annoying than crackling audio.

I've also tried 3-4 cables, and they're all about the same.

I've noticed that my audio only cuts out and sounds crackly with some TVs. For some reason, changing the resolution seems to fix the issue (at least for as long as I have my Steam Deck plugged in). This is with both the official dock and a cheap Anker dock.