Q: What causes black dust on the front wheels?

Hi there:

First off, the black dust on your front wheels is brake dust, which is created as the brake pads are applied to the rotor and stop your Subaru. This creates heat and friction which causes them to actually burn; giving off a black dust which collects on the wheels and brake pads themselves. The grinding noise is most likely caused by the brake pads being worn out and needing to be replaced as soon as possible. If they are worn out, they will eventually damage the brake rotors and could create a serious safety issue. To be safe you might want to contact a professional mobile mechanic as soon as possible to have them replace your front brake pads and see if your brakes require additional service.