While it could be software, it does seem to me that we're looking at a hardware issue. Speakers themselves, or the amp. Neither is good, and that would best be handled by a warranty replacement, if eligible.
You could try forcing the software download again, just in case some corruption is the source; I doubt it, but you can check again to be sure. If you want to go that route, try this:
HOME x5 FF x3 RW x2
Scroll down and select Update software. That will force a re-download of the current software.
Note: Don't mess around with the other stuff. There's a problem with your Roku TV right now. Don't make it worse.
If that doesn't resolve anything, a factory reset might, but I'm kinda doubtful. Again, it may be worth trying just in case, rather than the hassle of getting warranty replace/repair done.
DBDukes https://www.dbdukes.com/Roku Ultra (4660) Roku Streambar (9102) Roku Streaming Stick+ (3810)