Many noises that are reported as coming from the rear axle may actually originate from the following sources:

Perform a thorough and careful inspection in order to determine the source of the noise before disassembling the rear axle. Noise that originates in other places may not be corrected by adjustment or replacement of parts in the rear axle. Rear axle differential gears (like any other mechanical device) are not completely quiet. Rear axle differential gears should be accepted as being commercially quiet unless some abnormal noise is present.

In order to perform a systematic inspection for axle noise under standard conditions, perform the following steps:

1. Inspect the rear axle lubricant in order to ensure the correct level.
2. Drive the vehicle far enough in order to thoroughly warm up the rear axle lubricant.
3. Select a level asphalt road in order to reduce tire noise and body drumming.
4. Note the speed at which the noise occurs.
5. Stop the vehicle.
6. With the automatic transmission in NEUTRAL, run the engine slowly up and down through the engine speeds, corresponding to the vehicle speed at which the noise was most pronounced in order to determine if the noise is caused by exhaust, muffler roar or other engine conditions.
7. Tire noise changes with different road services, but rear axle noise does not. Temporarily inflating all of the tires to 345 kPa (50 psi) (for test purposes only) alters the noise caused by the tires but does not affect the noise caused by the rear axle. Rear axle noise usually stops when coasting at speeds under 48 km/h (30 mph). Tire noise continues but with a lower tone as the vehicle speed is reduced. Rear axle noise usually changes when comparing drive and coast, but tire noise remains about the same. Distinguish between tire noise and rear axle noise by determining if the noise varies with various speeds or sudden acceleration and deceleration. Exhaust and axle noise show variations under these conditions while tire noise remains constant and is more noticeable at speeds of 32-48 km/h (20-30 mph). Inspect for tire noise by driving the vehicle over smooth pavements or dirt roads (not gravel) with the tires at normal pressure. If noise is caused by tires, the noise will noticeably change or disappear and appear again with changes in the road surface.
8. Loose or rough front wheel bearings will cause noise that may be confused with rear axle noise. Front wheel bearing noise does not change when comparing drive and coast. Light application of the brake pedal while holding the vehicle speed steady often causes wheel bearing noise to diminish, because this action takes some weight off the bearing. Inspect the front wheel bearings for noise and looseness by jacking up and spinning the wheels, or by shaking the wheels in order to determine if the bearings are loose.
9. Rear suspension rubber bushings and spring insulators dampen out rear axle noise when correctly installed. Verify that no metal-to-metal contact exists between the spring and the spring opening in the frame or between the upper and the lower control arm bushings and the frame or axle housing brackets. Contact at these points may result in road noise and normal axle noise which would not be objectionable if dampened by bushings.
10. Ensure that no metal-to-metal contact exists between the floor and the frame.

Rear Axle Noises

After the noise is determined as being in the axle, establish the type of axle noise in order to help in performing any necessary repairs.

Gear Noise

Gear noise or whine is audible from 32-89 km/h (20-55 mph) under 4 driving conditions:

Drive: Acceleration or heavy pull exists.

Road Load: Vehicle driving load or constant speed exists.

Float: Using enough throttle in order to prevent the vehicle from driving the engine, the vehicle slows down gradually but the engine still pulls slightly.

Coast: The throttle is closed and the vehicle is in gear. Gear noise is usually more noticeable at 48-64 km/h (30-40 mph) and 80-89 km/h (50-55 mph).

Bearing Noise

Faulty bearings produce a rough growl or grating sound, rather than the whine typical of gear noise. Bearing noise frequently has a cyclic hum at the bearing RPM. This noise indicates a bad pinion or a bad rear axle side bearing. This noise may be confused with rear wheel bearing noise. Inspect and replace the bearings as required.