If it's an exhaust leak... and I'm not certain how you would do this on the 6, but when my Diesel Truck had a difficult to pinpoint exhaust leak, they did a smoke test. Used the exhaust back pressure sensor bung to inject smoke from smoke machine. I've also used the old rubber hose (3/4"or 1") stethescope to listen for leaks, but difficult in the newer tightly compact engine compartments. Hope you find it. Good luck.