Exhaust fumes circulating into car cabin.

Okay so maybe somebody started to steal your catalytic converter they have a slice in the pipe but didn't get to finish because they got interrupted You wouldn't necessarily hear that as much as you would smell it. So let's say that's not happened and your car's garage and the cars in perfect condition etc The next thing to look at is back at the muffler where the muffler exits the end of the pipe at the end of the car right there near the rear bumper cover If you go back lay on the ground on a piece of cardboard and look up at the exit of the muffler where it turns down underneath the bumper cover now look in the center of the car where the spare tire goes but you can't see that spare tire because you're under the car looking up at the sheet metal bottom of the spare tire well you'll see two rubber plugs are both of those rubber plugs installed and intact touch them does one just move over to the side like it's not even plugged into the hole exhaust gas can leak up into one of those holes if the rubbers not intact usually it'll be the one that's almost to the rear of the spare tire well that plug will be missing sometimes it's just laying in the floor underneath the spare tire If it is lift up the spare tire by unscrewing the big round gray nut lift up the tire put the plug back in correctly go for a drive and see if that stopped the smell? Usually I leave the forward plug in the spare tire well out just laying in the well so that water that passes through the seal of the hatch and drops onto the floor of the spare tire well and of the area where the battery goes that water will pass through The exhaust gas usually doesn't find its way to the hole that's on the forward part of the spare tire well but it will if the hole is uncovered at the rear of the spare tire well in California I would just make sure that both of those plugs are installed correctly and tightly because it never rains in California like the song said.