A worn pinion bearing will make a loud, grinding sound when the vehicle is in motion. This noise may be accompanied by vibrations that can be felt through the floor of your car or truck. It's important to pay attention to any noises you hear coming from underneath your hood, as they could signify a serious problem with your drivetrain. A grinding sound emanating from the pinion bearing could indicate that it is failing and needs replaced before major damage occurs. Generally speaking, this type of repair should not be attempted without professional assistance as incorrect installation or adjustment of components can lead to further costly repairs down the road. If you are hearing an unusual noise while driving, it’s best to have it checked out right away by an experienced mechanic who can quickly diagnose and resolve any issues with your pinion bearing..