In automobiles and other wheeled vehicles, the differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn. This is necessary when the vehicle turns, making the wheel that is traveling around the outside of the turning curve roll farther and faster than the other.  An increase in the speed of one wheel is balanced by a decrease in the speed of the other.

The rear differential is made up of many gears with teeth entwined with each other. The effectiveness of its function is dependent on how precise these gears are arranged and oriented relative to each other.   If, for example, lubrication runs low on the mechanism or the arrangement of the gears goes out of place, rear differential noise occurs. Gear whine, bearing noise and clunking are common rear differential noises that should be a concern to vehicle owners.

Rear differential noise, when ignored, can lead to major problems and permanent damage on the ring and pinion. Repair of the differential is usually recommended to be left in the hands of professionals because of the complexity of the system.