Thanks for the notes here. There are a few things you can try to see if this helps resolve that type of issue.
1. Replace the HDMI cable connecting your Roku device to your TV.
2. Connect your Roku device to a different HDMI port on your TV.
3. During playback of content inside a streaming channel, press the * key on your remote. A menu will open on the lefthand side of the screen. Look for 'Volume mode'. If this is turned on, try disabling or turning off this feature. Does that resolve the issue you are experiencing?
4. In Settings>Audio>Audio mode, try selecting 'Auto'. If already set to Auto, try selecting Stereo and see if the same issue occurs.
Keep us posted from there!