Re: Whining Noise on XJR
The rear axle has a large ring gear and a relatively small(er) pinion
gear. If their spacing isn't exactly correct their mesh will be "off"
and they'll be noisy at a specific speed, usually upon either
acceleration or deceleration. So if the noise always occurs at a certain
road speed, and usually in a 2 or 3 mph range, then it's probably the
ring and pinion mesh.
This can be corrected by adding or subtracting shims to move the pinion
gear ever so slightly forward or backward for perfect mesh with the ring
gear. There may be talk that the gears have already worn in and changing
their mesh is not advisable - that depends on the car's mileage -
because, yes they do have some wear now. The higher the car's mileage
the less advisable it would be to change anything.