Has the pylon structure possibly separated from the hull inside?
Yes.
Has anyone seen a hull fail for this reason?
Yes.
Two possible things:
1) The pylon shoe has become detached from the hull skin. You would notice a depression in the deck around the pylon fairing and possibly bulges in the hull sides directly beneath the pylon.
2) The pylon shoe is broken - the sides are still attached to the hull and the creaking you hear is the two halves rubbing against each other. This is most likely what's going on.
The solution involves major surgery - an access port needs to be cut in (behind the pylon is better structurally) and be prepared to be up to your shoulders in glass and epoxy resin as you reinforce the pylon shoe.
Unidirectional carbon fiber tows laid in an "X" pattern across the pylon shoe and along the hulls works well, but it's nasty work.
