I got some muffs and ran it for a while. I found the source of the clattering.
It's coming from right behind the prop, like you said. It only does it in
neutral. Every time it clatters you can see the prop hop forward a little.
When I engage it in forward it stops making noise and the prop starts
spinning. when I try to put it in reverse at low rpm it clatters even more.
If I turn up the throttle some it finally seems to drop into gear and starts
spinning in reverse. I'll look for those grease plugs like you said.

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