User blog comment:LeonTheDoge/Sea Dragon's roar/@comment-27538855-20160504231816

Not what I was expecting... We can eliminate the seadragon from the list of creatures that may be causing the strange void sounds...

The only creatures that can be making the noise are:

Sea emperor

Some unknown/in-dev/unimplemented creature

The sea dragon sounds like a huge elephant who is being forced into a cage