I have a similar problem. After watching Live TV the audio lingers and I get the live tv audio even when on a different app.
Nothing else is attached to the tv and “system restart” takes care of it until live tv is used again.
I’ve tried all the audio settings and nothing seems to work. I have the latest update on Roku and on my Sony tv. Cec is enabled and I’m using the earc input.
it’s definitely a Roku problem because the unit is outputing the sound.