Harmonic drone at 4k rpm (381 hours)

[Trevor23LSV]

First post here,

I am having two issues. First, my hull is collecting transmission fluid and it looks like it might be coming from where the tranny is bolted up at the back of the motor. It could be coming from somewhere else but I noticed atf fluid at the top of the bell housing. It is a ZF 45 CW. Not sure what it takes to further address this or what recommendations are out there. I am thinking for now to leave it. I would like to know if anyone has the slightest idea where to check. 

Second issue, at approx 4,000 rpm when cruising (340 Monsoon) I am hearing the slightest rhythmic drone. When i turn the sound goes away but once straightened out its back. I haven't heard it at 4,000 rpm in neutral but then again I did it for a brief time. As soon as I back off it goes away and when towing a surfer or wakeboard sound. Can anyone ecall having this peculiar sound coming out of the back? 

 

[formulaben]

Can't speak about the trans fluid, except that I'd drain it all and refill with new fluid per owner's manual. 

As for the sound, it could be prop sing, rudder cavitation, a bad cutlass bearing, a loose strut, or a loose tracking fin.  I'd inspect the prop for any small nicks or damage first, then while down there check the rudder for the same, then check the free play of the prop shaft, the rudder shaft, the strut, and then go forward and check the tracking fins.  All should be firmly attached with almost no movement. 

Your title says 381 hours, but is that overall, or just a new(er) engine?

[ahopkins22LSV]

I’ve seen a loose tracking fin cause a noise like that. I was also in the boat when the fin let loose. A lot of water came in very quickly. Luckily we were near the boat lift. 

[Trevor23LSV]

hmmm, track fins, didnt think about that. I will check into. Appreciate the feedback.

[Woodski]

@Trevor23LSV - ATF leak may be front trans seal, the flywheel is catching it and spraying it around.  Can you pop off a bellhousing plug and look inside to see if fluid is being flung around in there and then seeping out of any gaps / seams?  Could also be a cooler line coupling if near that area.  The two could be related if the trans is vibrating the shaft to cause the seal leak.  As noted all suggestions above are good possibilities.