I would offer it is not the Orion, it may be the slip splines on your driveline, since its out, pull the slip yoke apart, grease/coat splines with old school drum brake wheel bearing grease, was/is your drive line in phase ? phase it correctly, reinstall & test, I bet noise/vib gone. The preload Mark refered to is set by the amount of shims under the rear output housing, if it is incorrect it will cause a too tight bearing burn up situation, if it is too loose it could cause the rattle you mention. Take the e-brake drum off and hope there is no movement possible of the output shaft ?