I was driving along and noticed an exhaust smell with the windows up. It got quite annoying. I drove home and popped the trunk to check for holes and found two valved trunk vents. They are located inside the trunk in between the tail lights and behind a plastic cover. I removed the cover and looked closer and noticed the rubber flaps were long gone. I made new flaps out of rubber from an inner tube and the smell is now gone. I've seen a few posts here about this issue and posted this to help. I don't know if other models have similar vents.
WG