Sim, como Takkat disse, remova o ['YouTubeyoutubecom.desktop']
de com.canonical.indicator.sound interested-media-players
Usando algum script de shell:
#!/bin/sh
// Get current value
val=$(gsettings get com.canonical.indicator.sound interested-media-players)
// Remove youtube
new_val=$(echo $val | sed -e "s/YouTubeyoutubecom.desktop//g")
// Set to the new expected value
gsettings set com.canonical.indicator.sound interested-media-players $new_val
exit 0
Ou simplesmente usando o editor de dconf ...