I can hear a humming noise coming from the rear differential of my truck.
Hi there. A humming noise usually indicates a worn pinion bearing or an incorrect backlash setting on the rear differential between the ring and pinion gear. Sometimes, if the pinion bearing develops play due to wear, the pinion gear will move away from the ring gear creating excessive clearance and a gear whine. The pinion preload and pinion depth will need to be checked and a contact pattern check completed.