Bearing Whine
Howling or whining of the ring gear and pinion is due to an incorrect gear pattern, gear damage or incorrect bearing preload.
Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by worn/damaged pinion bearings. Bearing noise occurs at all driving speeds. This distinguishes it from gear whine, which usually comes and goes as speed changes.
As noted, pinion bearings make a high-pitched, whistling noise, usually at all speeds. If, however, there is only one pinion bearing that is worn/damaged, the noise may vary in different driving phases. Pinion bearings must not be installed new unless they are scored or damaged, or there is a specific pinion bearing noise. A worn/damaged bearing will normally be obvious at disassembly. Examine the large end of the rollers for wear. If the original blend radius of the pinion bearing has worn to a sharp edge, a new pinion bearing must be installed.
A wheel bearing noise can be mistaken for a pinion bearing noise. On 2-wheel drive vehicles, check the wheel bearing for a spalled cup and spalled/damaged rollers. Install a new wheel bearing if any of these concerns are detected.
If the wheel bearing is damaged, the roller surface on the axle shaft may also be damaged. Install a new axle shaft if any damage is detected.
On 4-wheel drive vehicles, check the wheel bearing for rotating smoothness and end play. Install new as required.