Thanks Weld, didn't know you had to get so far into the engine before gaining access to the shaft assemblies in the tranny. That's a good intro to the project that lies ahead...
I've heard on another forum that the noise can be a tolerance issue on one of the gears. If the issue happens in 3rd I suspect it could be the interaction between the 1st gear on its shaft when decoupled and free spinning. It could be hitting a resonance. 1st up I'll ride it some more, get a video with sound, and see if the magnet in my drain plug shows anything interesting...
Kelly