A Satyr Elder with panpipes spawned. They can put players to sleep and kill them while sleeping. Taking a rage potion will avoid this.
The panpipes make a pleasant tune normally, a merry tune when tipsy, a boisterous tune when seeing double, and a noisy tune when enraged.
This is the type of song which I imagine it sounding like:
And here's some real panpipe sounds for those who haven't heard them: