I've been trying to find what I thought was a fuel smell. When idling I could hear what was possibly an exhaust leak in the engine compartment. I have a mechanic's stethoscope. I pulled the pointy probe(that you would normally touch to parts) out of the single tube and replaced it with a 12" length of steel 3/16" brake line. It works great for locating "soft" noises like exhaust leaks. I located a leak under the tin shield of my rear exhaust manifold. I can only imagine the manifold is cracked under the cover. Is this common at all?