Hi, I just joined. Just wanted to add some more positive result in that I resolved pops and clicks by rpi-update to version 5.15.32-v7l+ same as @steveb. My setup currently is a pi4 with audio over USB to a Steinberg UR44C. Prior to this I was getting xruns with a variety of jack options, including:
-r 44800 -p 1024 -n 3
With the update, I experimented briefly and settled on the following which works fine:
-r 44100 -p 128 -n 3
Did you mean 48000 or 44100 here? 44800 is pretty wild.
We walk on the wild side here in Zynthian land. Indeed it is like the wild west at times!
@SHr00m welcome to the community. I’m glad you benefited from this. Note that the next major release of Zynthian (codename Oram) will be based on the 64-bit version of Debian Bookworm which currently uses kernel 6.1.21. There was an improvment to USB Audio in kernel 5.x which you would have seen in 5.15. There are further improvements for latency in 5.16. We should benefit from these in the next major release.
Appreciate the detailed update. Certainly looking forward to this.
@Baggypants oops, typo 
. It was 48000 
Easily done!