- A humming noise in the differential is usually an indication that the differential needs to be checked and inspected for gear backlash, gear wear, or bad bearings.
- Gears can whine or emit a howl - a very loud, continuous sound. Howling is often caused by low lubricant in the drive axle housing. The meshing teeth scrape metal from each other and can be heard in all gear ranges. If topping the lubrication level does not alleviate the howling noise, the the differential drive pinion and ring gear must be replaced.
Check the final drive's lubricant level when unusual noises are coming from the unit and as part of a preventative maintenance program. Courtesy of Nissan American.
- If a whining is heard when turning corners or rounding curves, the problem might be damaged differential pinion gears and pinion shaft. This is caused when the inside diameter of the differential pinions and the outside diameter of the differential pinion shaft is scored or damaged. The damage is usually caused by allowing one driving wheel to revolve at high speeds while the opposite wheel remains stationary.
- Another gear noise that is common in differentials is the chuckle. A chuckle is a low "heh-heh" sound that occurs when gears are worn to the point where there is excessive clearance between the pinion gear and the ring gear. Chuckle sounds occur most often in the deceleration mode, particularly below 40 mph (65 km/h). As the vehicle decelerates, the chuckle also slows and can be heard all the way to a stop.
- A knock or a clunk is caused by excessive wear or loose or broken parts. A knock is a repetitious rapping sound that occurs during all phases of driving but is most noticeable during acceleration and deceleration when the gears are loaded.
- A clunk is a sharp, loud noise caused by one part hitting another. Unlike a knock, a cluck can be felt as well as heard. Clunks are generally caused by loose parts striking each other.