One of the most common causes of a grinding noise when turning is a worn out constant velocity (CV) joint, which helps power the wheels on front-wheel drive vehicles. Another possible cause is worn out axle bearings, leading to metal grinding on metal.
A failing CV joint can eventually cause one wheel to lose power and even disable the vehicle completely, so it is important to have this problem checked out immediately. Similarly, a failed axle bearing can lead to a huge number of other problems and costly repairs, so it is best to have it replaced as soon as possible. In fact, all grinding noises coming from a car can be signs of a potentially serious problem and should be immediately checked out by a mechanic.
If a grinding sound occurs when slowing down or coming to a stop, it could be something as minor as a small rock lodged between the brakepad and rotor. Brakes normally begin to squeal when the brakepad wears down. However, when they begin make a loud grinding noise, it is a sign that the brakepad is completely worn out. This can lead to the metal backer clamping down directly on the metal rotor, which severely lessens braking power and can lead to costly repairs. If the brakes start making a grinding noise, they need to be immediately repaired, as this problem makes the vehicle extremely dangerous to drive.