Yep mine started doing that same thing about 2 months ago. I am at the point of making the roku a paperweight. For me it only happens in the xfinity app. I can watch disney or prime video it does not happen. While in the Xfinity App, suddenly the sound will start blasting and over drive the speakers. resulting in an extremely loud static over driven volume. if I back out of the channel, and go right back in, it fixes it for a while. its highly random, doesn't matter what is playing.
I've trouble shot the problem as much as I can, I disconnected the sound bar, that was using optical, and just used TV speakers, problem still existed. I've switched to HDMI cable inputs. Nothing changes. If I unplug the roku, and use the Xfinity app on my TV, no issues. that app suffers serious buffering issues right now, and that is the only reason the roku isn't a paperweight, yet. No reason to have a roku when it doesn't work.