The music player banshee which is part of the default Ubuntu setup pops up a message each time a new track starts playing.
To turn this off
- Open Banshee
- Go to Edit, preferences, extensions
- Enable Notification Area Icon
- The Icon should now show up - right click on it
- Uncheck Show notifications
- Disable the Notification Area Icon again
Very annoying - the option to turn off notifications is hidden on a menu you can’t get to by default.