Hi Doug,
 
Interesting note! We'll never know if the growl came from an animal, a
machine, a child's stomach, an offshore gas platform, a shrimp boat, or an
aircraft from Fort Eglin. It could even be gas escaping offshore from a
natural leak in the seabottom; I've read about that somewhere. Those are
truly eerie. It's thought that if a giant gas release (and they have been
documented in geophysical records) reached the surface directly under a
boat, the boat would sink instantly, no longer being supported by the
water. There would be no time for a radio message unless the operator were
already on the set, and he probably wouldn't know what was happening.
 
Keep on shellin', and don't let the sea monsters bite!
 
Andy
Andrew K. Rindsberg
Geological Survey of Alabama