2005 Kia Optima Exhaust problems

Every week or so I get extra exhaust coming out of my muffler, quite a bit actually. The extra exhaust smells foul. I've had a damaged E-vap canister for some time now and have never had this problem before. I have had the catalytic converter go out before and am concerned this may be the cause, but I am not sure.

I took the car into Firestone and they did a basic inspection but did not find a hole in the muffler or anything like that. Could the problem with the E-vap canister be causing a problem with the catalytic converter? A mechanic friend said that may be it. Honestly I am not sure what the issue is, I can only guess.

I have a 2005 Kia Optima as well and I get this same problem. It happens every 3 months or so. I have a problem with my E-vap canister as well, perhaps that is the reason. I have yet to get it diagnosed.