Non-Axle Noise

The five most common sources of non-axle noise are exhaust, tires, roof racks, trim mouldings and transmission.

Make sure that none of the following conditions are the cause of the noise before proceeding with an axle teardown and diagnosis.
- In certain conditions, the pitch of the exhaust may sound very much like gear noise. 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 and mouldings can cause whistling or whining noise.
- Clunk may be 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; 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 pinion bearings, which are operating at driveshaft speed. The front hub and bearing units or the rear cartridge bearings may whine the same way if they run completely dry. 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 wheel bearing. This lower pitch sound occurs because the wheel bearing turns at only about one-third of driveshaft speed.
- Wheel bearing noise might be mistaken for pinion bearing noise, so always evaluate the wheel bearings carefully before tearing down the axle. As noted earlier, pinion bearings make a high-pitched, whistling noise, usually at all speeds. However, if there is only one pinion bearing that is malfunctioning, the noise may vary in different driving phases.

Noise Conditions
- Gear noise is typically a howling or whining of the ring gear and pinion due to an improper gear pattern, gear damage or improper bearing preload. 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 vehicle speed.
- Knock is very similar to chuckle, though it may be louder and occurs on acceleration or deceleration. The teardown will disclose what service is required.
- Click at engagement is a condition when the axle produces a slight noise, distinct from a clunk, that happens in REVERSE or DRIVE engagement. Check for the presence of a pinion oil slinger.
- Rear hub bearing noise is similar to gear noise and pinion bearing whine. However, rear hub bearing noise will normally distinguish itself from gear noise by occurring in all driving modes (drive, coast and float), and will persist with the transmission in NEUTRAL while the vehicle is moving at the problem speed. If, upon ride evaluation, the vehicle displays this noise condition, inspect the rear hub for looseness (proper torque on hub nut), side-to-side play and leakage of grease. Correct as necessary. Re-evaluate the vehicle for noise before removing any internal rear axle components.
- Boom is a condition that exists when the ring gear teeth have a backlash variation of more than 0.10 mm (0.004 inch). Boom could also be caused by excessive rear axle flange runout or pinion pitch line runout indicated by excessive backlash variation or driveshaft imbalance.