When you're driving and turn a corner, you probably aren't aware of all that's going on with your wheels.  The outside wheels have a longer distance to travel than the inside wheels, so there are gears that allow the wheels to go at different speeds when you turn.  That set of gears is called a differential.  In front-wheel drive vehicles, it's by the transmission and called a transaxle.  Rear-wheel drive vehicles have the differential, naturally, on the rear axle. Many all-wheel and four-wheel drives add a center differential since power has to go to the front and rear wheels. (Some newer vehicles power wheels with electric motors, but that's a whole different story.) Time and distance traveled eventually can take their toll on the differential, and you may notice some noises you hadn't heard when your vehicle was newer.  Sometimes you'll hear a whir that might change in pitch when you turn.  You may hear clicking sounds when you're moving.  Others d ... read more