Knockers

Knockers are a race of minor Fey who live underground and are associated with mining and minerals. They are a short, slightly ugly race of humanoid creatures with exaggerated features and are known to 'knock' on the walls and timbers of mines in order to judge their strength (hence their name).
Knockers are shy and elusive but other members of the Order of Fey learned long ago to call upon them for their help and expertise when operating beneath the Earth. 
-http://self.gutenberg.org/articles/Knocker_(folklore)
Category:Fey