Hi. recently my car is making a grinding noise. i checked around the underside of the car but there is nothing dragging against the ground. Then i realized the noise is coming from the rear driver side wheel. It wasnt as bad before but now its really loud and aggrevating. It sounds like 2 pieces of metal are rubbing against each other. It only makes a noise when i am driving or reversing but when stopped, no noise. Anyone have a clue to what it might be and if it is still safe to drive my car. Thanks.