Axle Retainer Nut Torque w/ Green Bearings?

I would pull that third member and check the pattern snap some shots and will have a look see. It could be starting to finally break down to the edge of the gears meshing and will resonate a whine noise when coming off each other.

Bearings also can be checked with a tug in and out up and down and double check the backlash NO tighter than .005 no wider than .010 .

Good luck and hope to see some pictures.

IF you want to run a pattern and do not have marking compound you can use a girl friends or wives old bright lipstick or clown make-up some sort of grease colored paste.

Jim
J D Race