The closest I have to your issue is when using the Roku app with a Bluetooth speaker connected to the TV.
I get a few weird crackles and pops when I first launch the app and start to play something, but after a few seconds it goes away and doesn’t seem to come back until I start completely over again (TV/Roku/speaker rebooted). It’s the only time this happens and any other combination of viewing/listening works fine.
No idea if the Roku is on the eArch HDMI port or the secondary.
Great description of your issue. If you add which app (Roku/Android/Fire) and version you’re using, we can all help you figure this out, or at least find a way to replicate your problem.