I did the Sylvanas song event on my new belfmage. If you're not familiar with the quest this is what happens:
You find a medallion from Sylvanas' sister Alleria (who's in Outland and probably doesn't know that she's related to a dead girl now), and you bring it to Sylvanas. She summons these 4 banshees, and they sing this really pretty, sad song. This is the one and only time you get to hear the song.