Transmission Issue.

Well... out skiing last night, and everything is running good.. I pull the boat into neutral and there is a clunking noise coming from the back part of the boat.. around the prop shaft area.. I noticed it sounded off.. put it in neutral and rev'd it a bit seemed to go away. We skied back toward the dock, and I put the boat on the lift and checked the prob for tightness.. everything was good there.. pull the floor up in the back, and when i grab the prop shaft and twist it back and forth. there is a noticeable clunk. almost like a gear lash. I has never done this before, and will do it when the boat is in neutral like something is really loose in the bell housing/tranny. i can get a video tonight, anyone have any suggestions.. or thoughts.. It's 90 degrees here.. the water is like glass, and the skier balls are calling my name.. HELP!

This is what is sounds like.. this is twisting the prop shaft back and forth... in and out of gear.
http://www.youtube.com/watch?v=DWQnqT9k2os&feature=youtu.be

noise