Factual error: There is an explosion in the laboratory supposedly because the professor's assistant added too much aqua regia. Aqua regia will do a lot of things, but in an open furnace it will not explode.
Audio problem: Throughout the movie when they are underground, when someone speaks sometimes you hear an echo and sometimes you don't.
Factual error: Iceland has had no titles of nobility for nearly 1000 years, therefore Saknussem can't be a "count".
Answer: It's just an added sound effect that foreshadows an ominous event (the giant reptile) that is about to happen. It's not meant to be anything naturally occurring.
raywest ★