As far as I can tell, it's only happening when in gear. If I run the boat out of water and rev it up a bit, nothing. When we take it out to the water, it sounds fine in neutral, but starts making a high pitch whine or squeal when it's idling forward. Sound goes away when we bring the rpms up a bit.
I will take a recording of it while we are out this weekend if that helps.
Boat is a 2003 Centurion Avalanche with 6.2L Black Scorpion.