The medieval Germans called them knockers, and I've seen a couple of Youtube videos from mine explorers where they're down a mile or two and there are these knocking sounds coming from God knows where . I don't easily get creeped out but something about this did it.
Tolkien's orcs (and goblins, he uses the words interchangeably) lived in mountains. Notably Goblin-Town in The Hobbit. Here's the song "Down Down to Goblin Town" from the Rankin-Bass movie from The Hobbit (1977). You know you want to listen to it. They tried using men's choirs for all the goblin-songs to make them menacing, but they only succeeded in making them sound bad-ass. Go ahead and crank the sound up.
Fun fact: One of the singers of this song is none other than the legendary Thurl Ravenscroft himself. That's right, the voice of Tony the Tiger is on the bass part.
You go my lad! Ho, ho my lad!
The Mongols made such a tremendous impression because they mass murdered anyone who got in their way. They easily brushed aside the armored knights of Europe. They would have made it all the way to Portugal except for the fact that Ghengis Khan died and they were called back to Mongolia to decide on a new leader.