lately, my brakes having been making scratching noises even when i dont step on the brake. i jacked up my car and spun the back wheels to see what it could be and it appeared that the brake pad was rubbing on the piston slightly even though the brake wasnt depressed. what should i do? can the rust on the piston be sanded off or is there something special for it? thanks for the input

 

I'm assuming you mean brake rotor not piston. The brake pad contact surface of the rotor should be shiny if the brake is operating normally. If it is rusty it indicates the brake is inoperative probably due to a seized piston or stuck sliders. Even on normal brakes that are not applied it will appear as though there is little or no clearance between the pad and the rotor (and therefore the back of the pad/shim and the piston) Be aware that brake wear indicators (scraper/sqealer) will contact the rotor when the brakes are applied OR released if the pad is actually worn. I suggest you have someone familier with brakes look at them with you.