Hey, Ive been throwing a cat code every now and then for a while. It comes, it goes, it stays, it leaves lol.

-No Loss of Power
-No Smell
-No rattling
-CEL comes and goes
-Car is not exhaust leak loud, but appears to be a little throaty/deeper but not SUPER deep.

Here is a picture. Is this reason to believe there may be a leak here or is it just old down there?

 

I would say your OEM cats are going. Time for a custom full exhaust

 

if you dont hear any fluttering, or see any dark deposits then there is no major leaks. you can also spray some soapy water there and see if it bubbles up. is it the p0420 code? most likely just a o2 sensor if it is but worst case scenario would be the cat. a few folks on here tried swapping the cats to see if that changes the code to a different bank & even a few members here said their MAF sensors were slowly dying causing it to throw a cat code as well. if its not severe for your p0420 if you reset it it usually pops up again after another 150-300 miles.

 

There is a sound when you rev the engine in neutral as the rpms drop down, could that be decribed as a flutter? Also when the car is cold at idle, it seems as if there is engine noise under the floorboard on that side, well atleast it kinda sounds like it and my gf mentioned it. hmmm

 

i would spray some soapy water on it and have someone rev a little and see if the water starts to bubble or spit outwards. normally since its right at an angle do you notice condensation/water spots on the floor right at that area if your parked at idle for a while and drive away?

and with the flutter, it sounds like someone is forcing water/air at the same time out that leak area. *bup bup bup bup etc etc.* <-kinda sound like that lol.

 

My dad had a similar problem with his GS. He was throwing cat codes too. He took it to the exhaust shop and they said he had a leak behind the cat baskets (I guess where the cats and the y-pipe meet). He got them fix and had no codes since, and it sounds alot smoother at idle. So I would get that check out, your cats can still be good.