Let's create a creature with the ability to create a loud boom with only its body. We'll start with a terrestrial predator, that gives us a good reason as to why it needs to do this. It uses the thunderclap it creates to stun or, in the cases of animals with especially powerful hearing, incapacitate its prey or rivals. We'll also say that this creature resides on earth or a planet identical to it (maybe no humans). The creature will be roughly the size of a rhino. Now that we have a good place to start, let's do some research!
First up, the click beetle. Its Wikipedia page states:
Alright, that's a good possibility. Our creature can snap two special plates together to create the "thunderclap". But it would probably end up sounding more like a massive crack than anything. Or, perhaps the "thunderclap" isn't a direct result of two plates snapping together. What if our creature had two special plates on its back. One is firmly attached to the upper spine while the other is help on by powerful muscle and sinew. The second plate will have a protrusion perfect for creating that BOOM when it gets up to the right speed. How will it do this? By clicking the loose plate into the fixed plate and then flexing all those powerful muscles to build up massive amounts of potential energy in the plate. Then, the plate releases at speeds fast enough for the protrusion to break the sound barrier. It's an interesting idea, but let's look at another possibility.
Up next, Apatosaurus, This wonderful video demonstrates that apatosaurus might have been able to break the sound barrier with their tails. That's pretty amazing, but could a whip-like structure work on our predator? Let's speculate. Perhaps this tail isn't a tail at all, rather, it might be a long structure made of sinew and muscle near the base. We'll also say that this structure has bone near the base for the muscle to attach to. So now we have a creature with a whip made of sinew, muscle, and some bone attached somewhere on its body.
But now for the real question part of this post: How plausible are these ideas? Could this creature have sonic speed plates or flesh whips?