I have had this roku for about two weeks. Last night I kept having volume issues. It was as if someone was turning the volume up and down nonstop. I switched apps and it kept doing the same thing. I tried different volume modes and it did it not stop with leveling turned off, on, or night mode. All three modes, the volume was going up and down constantly. I never noticed this happening before and I have no idea how to make it stop. It's frustrating. It's not the tv itself. I have a new 4k express+.
Have you tried restarting your Roku?
These things are just special purpose computers. Like their big brothers sometimes clearing things out by restarting them can correct problems. (Note that if yours is a Roku TV with "Fast start" enabled, turning it off and back on just puts it into and out of a standby state and does NOT give you a complete restart.)
Depending on your Roku model and Roku version number you'll find the "System restart" option under "Settings > System > Power" or if not there, under "Settings > System”
If a restart doesn't do it, or if you don't have sufficient control with the remote to navigate the Roku menus, you can also restart by pulling the power plug to the Roku for a minute or so then plugging it back in.
I have completely restarted the Roku a few times and it's still doing it.