Ford 2003 Mustang Workshop Manual page 271

NOTE: A low-pitched rumble normally associated with a worn/damaged wheel bearing can also be
caused by tires.
A wheel bearing noise can be mistaken for a pinion bearing noise. Check the wheel bearing for a
spalled cup, and spalled/damaged rollers. Check the wheel bearing for rotating smoothness and end
play. 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.
Chuckle
Chuckle that occurs on the coast driving phase is usually caused by excessive clearance between the
differential gear hub and the differential case bore.
Damage to a gear tooth on the coast side can cause a noise identical to a chuckle. A very small tooth
nick or ridge on the edge of a tooth can cause the noise.
Clean the gear tooth nick or ridge with a small grinding wheel. If the damaged area is larger than 3.2
mm (1/8 inch), install a new gearset.
To check the ring gear and pinion, remove as much lubricant as possible from the gears with clean
solvent. Wipe the gears dry or blow them dry with compressed air. Look for scored or damaged teeth.
Also look for cracks or other damage.
If either gear is scored or damaged badly, install a new ring gear and pinion.