Where does Spirit of the Howler drop?

[Freakish]

I've seen it off guardian wurms in skyfire but those are level 60 mobs. Also seen it off juggs in trak lair. The reason it's so expensive isn't because it's impossible for a shaman to solo for it as it is that it's one of the rarer lvl 55 spells and very good so it's in high demand.