In speaking to a mechanic on the phone he said it could be the shaft zinc has come loose and the sound is traveling up the shaft and sounds as if it’s actually coming from the tranny.
Back when we did the short haul a couple weeks ago, I had commented to the broker that the zincs were in poor shape and there was no prop shaft zinc. He changed one of the tab zincs and put on a shaft zinc. I was busy working with the surveyor so I didn’t check his work – maybe it loosened up? I don’t remember him seating it with a mallet or hammer. Is the zinc to close to the prop? - is there a taper in the shaft at this point which would have caused the zinc to loosen? Here is a pic I took during the short haul which shows the newly installed zinc:

Well tomorrow I have to go out of town all day and then back to work Monday. It looks like I am gonna have to do a night dive in the beginning of the week to check that zinc. I have a drysuit and have dove in Feb in 37deg water so not exactly what I feel like doing but not really too big a deal until I get out of the water, that's when it gets ugly, especially cleaning the dive gear... Plus it's a lot work for a week night but this is gonna bother me.
Could this be the cause of the noise? When I was listening carefully to it it sure sounds like it's the kind of noise that would result.
It only makes the noise in fwd, not reverse. Maybe in fwd the loosened zinc is hitting up aginst the prop but in reverse it's pushed away from the prop up against the strut?? I would think the zinc would have just fallen off if it loosend up.
She's a 2000, the fluid is clean and at proper level and she’s only got 450 original hours? Although possible, a major problem is unlikely. From what I've learned these reverse trannys are quite tough.