Factual error: The Sun was shining quite brightly on the shores of the underground ocean (near the center of the Earth) as can be seen by the shadows of the actors. (01:39:20)
Factual error: Iceland sure looks a lot like the California desert.
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.
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 ★