It sounds like the mesh of the ring and pinion gears was not adjusted; or not adjusted properly. These parts must be checked by applying prussian blue or a comparable compound to the gear teeth, and then rotated to show the location of the contact area. The contact is then adjusted with shims to alter the mesh. They cannot just be replaced and be expected to fit properly without adjustment. If the units were not refilled when they were reassembled, or the proper lubricant was not used; this could also create the noise.
It also might be worthwhile to put the vehicle up on a lift, and run the speed up to over 65 mph; to see whether the noise can be heard when the wheels are off the ground. If there is no noise when the wheels are off the ground; the noise is probably coming from the tires.