It turns out that goblins and wolves yammer, as do dwarves in their presence.  Yammer, yelling or shouting, has an earlier obsolete meaning in the Oxford English Dictionary – specifically to make that noise in mourning and lamentation.  Yammering in The Hobbit occurs only in the context of goblins and wolves.

• 04.021 Batter and beat! Yammer and bleat!
• 04.022 and more than one of the dwarves were already yammering
• 04.036 The yells and yammering,
• 06.065 and yammering
• 06.082 The wolves yammered

“yammer, v.”.  OED Online. Oxford University Press, March 2015. Web. 9 May 2015.