It sounds like the dogs are barking in this transmission - similar to the sound a bike makes when a rookie pushes down too slowly on the shifter peg while the bike is running.
The racket happens in neutral clutch in or out. Sometime first, but only with the clutch pulled in. Under load it is quiet. It does not slip out of gear (yet) and neutral is easy enough to find (most of the time).
I suspect a bent fork is causing a dog fight in there but was hoping somebody had another viable theory?