"Well, that was easy..." Buckthorn will look (perception) in the hallway to try to discern (dungeoneering / nature) what kind of creatures he heard scampering away. He will look for tracks or any other indications - spoor, bones, etc. - to try to determine what creatures where living here. Also, does the party still hear music? If he still hears music, he will cover his ears, following Ghen's suggestion, and suggest the other party members do the same.