Type the following, line by line, in your terminal:

amixer set Master,0 100%,100% unmute
amixer set PCM,0 100%,100% unmute
amixer set Line,0 75%,75% mute captur
amixer set Capture,0 100%,100% captur

This will fix any issues you have with sound still playing whenever you’re not watching tv, and probably sound sync issues as well. It did for me. Found here.