These could be the underwater equivalent of the sound of wind in a cave.
Powered by volcanic emissions instead of wind. Depending on the shape of the orifice and the size/shape of the chamber, it could make any kind of sound.
I was thinking of filtering of the random noise by features in the environment as well - perhaps thermal gradients in the water setting up reflections &c.
Powered by volcanic emissions instead of wind. Depending on the shape of the orifice and the size/shape of the chamber, it could make any kind of sound.