For what it's worth, my SL is straight K-jet (no emissions controls) and no cat (Euro model). On startup, you can definitely smell gas when the cold-start injector is open. I run it on the lean side, and when warmed up, you can still faintly smell gas. Still get in the mid-20s on the road though. It could just be that without the cat, you smell the fuel.

I'd be leaning more towards a defective cat than anything else. My dad's 2012 F-150 3.7L V6 had a really irritating rattle. Took it to the stealership and the driver's side cat was damaged (broken away internally). Truck still under warranty, 13K miles on the clock.