When I stomp on the brakes ... I hear a "gush" of air and the pedal travels 2-3 inches before I get response at the wheels. Is there some sort of piston or something between the brake pedal and the booster? Could this be related to the check valve at the booster? Sound is loud and definitely under the dash, not behind the firewall. When letting up on the pedal I hear a squeak behind the firewall sounds like air leaking more than hydrolics. Any suggestions?