Check the audio settings on your set to see if they’re set correctly or not. If that doesn’t work, you may need to contact the TV manufacturer, knowing that Roku doesn’t make the RokuTV sets themselves.
I’m tagging @Hector-Roku, so that he can help you more about this issue.
I’m into videotapes and old electronics stuff, including extenders, converters and analog 4:3 TV sets (which are obsolete these days), and Miss Bianca is my favorite character in Disney’s The Rescuers (1977) and its sequel, The Rescuers Down Under (1990). I am not a Roku employee, only a user like you. ~ Jordan