I have a 1992 f250 4x4 with 215k miles. The 1356 tcase was making some racket and light vibration at speeds around 30 and above with either the hubs locked or just the tcase in 4 high. The faster the worse it gets. I tore it apart and replaced all bearings and seals leaving the chain untouched because it seemed ok. With the truck off the ground and in gear running it seems the noise is coming from the shaft attached to the front driveline. I did remove the front driveline to remove that as a possibility... is it possible the chain can seem ok yet cause such problems? not sure what else it could be