Recently, my 2003 996 C2 is making this crazy racket at idle. There is no check engine light (CEL) coming on, so I thought maybe it was just the exhaust. I ordered the cargraphic sport exhaust as well as a new IPD plenum (have been looking for an excuse to put some mods on). But after reading the following thread, I am wondering if it is the cats. From what I read it sounded like bad cats always were acompanied by a CEL, but maybe I missed something.

https://www.6speedonline.com/forums/...rket-cats.html

Is there anything else that I should be considering that could make such a racket? It seems to go away when I get up above 1.2k RPM on the motor. But I seem to be able to make a kind of "chunking" sound by quickly, but slightly increasing the rpm on the motor. I know it isn't knocking, or pulleys, and have isolated to the exhaust, so I am pretty sure it is an exhaust/cat issue.

Sorry in advance for the strange description of sounds, I will try to attach an mp3 recording of the sound when I get a chance.

 

I had a similar problem. It was the exhaust tips (stock).

Previous owner scraped them several times and broke an internal weld.

You can do a little tapping with a rubber mallet to figure it out.

 

I'll go check it out right now. Lat year, while going to a DC United Game they made me park on a hill. Backing up, it slightly scraped the tips on the bottom. I'll let you know.

 

Well, I finally got my head up under the car (did it before it got too hot) and it definitely is the cat. So now I am off to the dealer to get my new cats. Should still be under warranty from what I read, since the car is only 6 years old and the car has less than 30k on it. What I may do is just get new factory ones installed, if I can for free, then when I do the Cargraphic exhaust, pull them off and put on after market ones. If it goes down this way, I will have a very, very nearly new set of cats for a 996 for sale. Though I am not sure if they are compatible with any of the 3.4L 996s who might be out of warranty.

 

You might get some gripe from the dealer because you do not have the CEL on.
Hopefully not, but heard it happens.

Oh and btw, the cargraphic sounds *****in with the stock cats.

 

Thanks! Good to know both about the dealer and the stock cats. Maybe I won't do the after market ones.

Dropped it off today, so we'll see what they say. I mean it sounds awful and loud. So bad in fact that I am embarrassed to stop at a light with it. It sounds like I have marbles in a can shaking randomly.

I'll let you all know what Hunt Valley Motors in Maryland does for me.

 

Is it just the heat shield? That wont trigger a CEL and is most likely your problem.

My guess is they repair the heat shield. My final answer, lol

 

Valley Motors says it is the catalytic converter and are replacing it gratis. Nice!

 

Nice... you realize how much those cost right? so in all fairness you owe your car the same amount of $ in mods. it is the least you could do.

 

Holy crap! Just looked online and found them for $1100.

So now, the dollar for dollar price match. Have the exhaust and plenum. Now I guess an ECU upgrade? Maybe go higher and get the headers? Been really kicking around replacing the seats with carbon fiber seats, saves a ton of weight I guess. Maybe some other parts to update the interior a little.

Any ideas certainly appreciated.