The correct answer to this open question is the following.
A blue whale is louder than any animal around.
Go in search of a thing that also makes a loud sound.
Well, talking abound animals sounds, what about the roaring of a lion or a tiger. That is loud too, and scary.
If we do not want to refer to an animal sound, we could talk about the sound of the turbines of an airplane. That is loud. Indeed, floor airport operators have to use earplugs or other kinds of protection to avoid ear damage in the workplace.
The sounds of machines in many industries and factories are also very loud.