Axle Noise

DESCRIPTION
The following is a glossary of axle noise terms:
- Gear Noise is the typical howling or whining of the ring gear and pinion. It can occur at various speeds and driving conditions or it can be continuous.
- Chuckle is a particular rattling noise that sounds like a stick against the spokes of a spinning bicycle wheel. It occurs while decelerating from 64 km/h (40 mph) and can usually be heard all the way to a stop. The frequency varies with the speed of the vehicle.
- Knock is very similar to chuckle, though it may be louder and occurs on acceleration or deceleration. The teardown will disclose what has to be corrected.
- Clunk may be a metallic noise heard when the automatic transmission is engaged in REVERSE or DRIVE, or it may occur when throttle is applied or released. It is caused by backlash somewhere in the driveline or loose suspension components. It is "felt" or heard in the axle.
- Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by malfunctioning differential pinion bearings, which are operating at driveshaft speed. Bearing noise occurs at all driving speeds. This distinguishes it from gear whine which usually comes and goes as speed changes.
- Bearing rumble sounds like marbles being tumbled. This condition is usually caused by a malfunctioning rear wheel bearing. The lower pitch is because the rear wheel bearing turns at only about one-third of driveshaft speed. Wheel bearing noise may also be high-pitched, similar to gear noise but will be evident in all four driving modes.
- Chatter on corners is a condition where the whole rear end vibrates only when the vehicle is moving. The vibration is plainly felt and heard. In conventional axles, extra differential thrust washers cause a condition of partial lockup that creates this chatter. Chatter noise on Traction-Lok(r) axles can usually be traced to erratic movement between adjacent clutch plates and can be corrected with a lubricant change.
- Click at engagement is a condition on axles of a slight noise, distinct from a clunk, that happens in REVERSE or DRIVE. It can be corrected by installing a slinger between the rear axle universal joint flange and front pinion bearing.
- Axle shaft noise is similar to gear noise and pinion bearing whine. However, axle shaft bearing noise will normally distinguish itself from gear noise by occurring in all driving modes (DRIVE, COAST and FLOAT), and will persist with transmission in NEUTRAL while vehicle is moving at concern speed. If the vehicle displays this noise condition, remove suspect axle shafts, replace inner wheel bearing oil seals, and install a new set of axle shafts. Re-evaluate vehicle for noise before removing any internal components.

NON-AXLE NOISE
There are a few other conditions that may sound like axle noise and must be considered in pre-diagnosis.
- The most common are exhaust, tires and trim mouldings.
- In certain conditions, the pitch of the exhaust may sound very much like gear whine. At other times, it can be mistaken for a wheel bearing rumble.
- Tires, especially snow tires, can have a high-pitched tread whine or roar similar to gear noise. Radial tires, to some degree, have this characteristic. Also, any non-standard tire with an unusual tread construction may emit a roar or whine-type noise.
- Trim, grille and mouldings can also cause whistling or whining noise.
- Make sure none of these is the cause of the noise before proceeding with an axle teardown and diagnosis.