I would appreciate any advice anyone could give me. When I am braking, I hear a distinct hissing/echoing sound in throughout my car. I am sure it is the brake system, as it only occurs while braking, but I cannot tell if it is coming from the front or the rear. It is not a screeching that would indicate low pads, and I checked the pads in front...They seem fine. It also does not sound like the pads scraping the rotors. Could this be a fluid problem? Please advise. Thanks all.