I have the same problem. In fact sometimes I completely lose all audio. The fix for me is to unplug the Roku Premiere box for a few minutes and then plug it in again. Then everything is normal until the issue happens again which usually is within a few days.
I've started seeing this same problem since I purchased a new (Vizio) TV and connected my Roku Express to it. No problems with my previous Sony TV at all. No idea why the new TV would make the difference.
I've tried all the suggestions regarding audio settings - they don't fix the problem. I've even tried something I saw recommended elsewhere - plugging headphones into the headphone jack on the back of the TV, which forces the TV to adjust its audio settings, and then unplugging them - that didn't work either.
The only sure-fire fix for this (at least for me) has been to restart my Roku device by going to the Home menu, Settings, System and Restart. But that's a band-aid fix - it only works temporarily. I don't really want to buy a new Roku device and have the same thing happen, but I'd love to get this fixed permanently. It was never a problem in the past, only since the new TV - that's the only variable that has changed in my setup.
I've contacted my internet provider, my internet is fine. I've tried contacting Roku but they are not answering phone calls during the pandemic. I had to email them. Meanwhile my roku tv sound is awful. Its crackly and static. I've uninstalled and reinstalled my roku tv. This happens with my other two tv's as well. They both use the Roku Premier. I bought a Roku tv thinking it would have better sound. I was wrong.
I too have been having the same issue for about a week. My roku is a couple months old. I've been thinking the speakers were about to go out on my tv. I tried the whole menu volume off thing and it did not work.
I then went to audio settings and changed the audio mode from "auto(DD)" to "stereo", and it seems to have fixed the issue....for now. I even went back and changed it back to auto, and so far i am not hearing that distorted sound. Hopefully this resolves the issue.for good. We shall see.