[noggin]

This doesn't seem to be related to Kodi as the same issue occurs for every sound output regardless of the program used. Even speaker-test displays the same problem.
It could be the AVR, I'm not sure as the same setup works fine with a Pi2, only the Pi4 seems to have this issue.
I posted the problem with more detail on the raspberrypi forums: https://www.raspberrypi.org/forums/viewt...8&t=273949

I also tried to patch the kernel with the following thinking it could be related but I was wrong. https://github.com/raspberrypi/linux/com...e57464497e

Thank you for the repost.
I am afraid I wasn't very precise:
I do occasionally use the mentioned formats, however it seems to happen most notably during AAC (PCM) with or without passthrough as far as I can tell. I have not observed it in DTS yet. As Puck says it is hard to reproduce. Please excuse my inexperience, I am trying my best.
I have used AAC-Videos with passthrough via HDMI with multiple devices (Blu-ray Player, Win7/Win10 Laptops) and I never encountered this phenomenon. As far as I understand, it is not very likely to be an issue of the AVR.   

AAC and PCM are not 'passthrough' formats (*) - so they can't be passed through. AAC is decoded to PCM, and PCM is carried as PCM - which is a baseband format that is treated differently to a bit streamed format that is just passed through untouched.  So the passthrough response was a red herring - as you aren't playing formats that could be expected to be passed through. 

I'm going to guess you don't get it with DD/AC-3 or DTS content that can actually be passed through.

So the issue is likely to be to do with the way the Pi 4B handles multichannel PCM output.