If your car is newer, it transmits power to the wheels through flexible axles, called Constant Velocity Joints, attached to the drive shaft. These are covered with rubber boots packed with grease to keep debris out of the joints. If the rubber boot gets damaged, this protective grease gets out and moisture and dirt get into the joint, causing it to fail. Caught early, you may only need to replace your boot; most often, however, the entire axis needs to be replaced. If you hear a clicking or popping noise when you are turning, this could be the problem. Try to reverse in a circle and see if this makes the noise louder—if it does, you need to get your car in for repair soon.