Knocker

Most frequently described as a small humanoid approximately 80 cm in height, the Knocker (or Rapper, Kobold) resembles a small hairy ape. It is assumed to be a subterranean creature that has various magical powers attributed to the Faerie creatures. They are miners by nature, and often excavate new mines and explore tunnels for unknown reasons. Folklore suggests that they live in hierarchical, rigid societies, and that they are capable of great physical effort with very little sustenance. They avoid all contact with metahumanity, using their considerable magical powers to do so, and thus have been hard to study and observe.

(Paranormal Animals of Europe)