Is it even possible for something to grow that size on this planet? The Blue whale is currently (to the best of my knowledge) the biggest known living "thing" on this planet. A few Dinosaurs have been bigger but not too many. THIS THING?? Good Lord. Makes me wonder if this planet has a built in size limit for anything living.
I think it might be the Leviatan of the Atlantis movie (at least one of them in the prologue there was like three or four), Cthulhu because the sound was detected very near of the coordinates where is the city where he is sleeping, might be Godzilla, might be many things or nothing