when i driving slowly or fast i can hear a lous hissing noise for a little then it stops and then starts when i start to drive again, im not sure it its the brake pads or my rotors? any one know what the problem might be, i know my brkae pads are going out pretty soon, they start to make the screech noise a little also. but that noise i know how to fix, but the hissing noise im not sure.