Have you tried latencymon? Does the crackle/pop etc correspond to a spike in system latency? It also lets you know which process caused the spike to narrow down the culprit.
Latencymon shows everything fine with the browser up.
Once I minimise the browser and the audio issue starts LM changes to...
Your system seems to be having difficulty handling real-time audio and other tasks. You may experience drop outs, clicks or
pops due to buffer underruns. One or more ISR routines that belong to a driver running in your system appear to be executing
for too long. One problem may be related to power management, disable CPU throttling settings in Control Panel and BIOS
setup. Check for BIOS updates.
...and points to HDAudBus.sys and Wdf01000.sys, both Microsoft system drivers, as having issues.
But I guess this is a symptom of the card not outputting audio properly at low load, rather than these drivers being the cause.
PCIe is forced to Gen4 in the BIOS.
When first installing the card this was on auto, audio was totally bugged, noticed GPU-Z reporting it flicking to 1.1 and back.
Forcing it to Gen4 fixed that.
Running AMD Ryzen High performance power profile.
PCIe Link state power management is confirmed off.
Now that I know I have enough connectors on the PSU, I'm half thinking to test installing a 2nd older GPU and just swap the cable between each to see/hear the difference.