Very LOUD rattling from exhaust...CAT??? [Archive] - Forum


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10-27-2004, 10:57 AM
I've had this really loud rattling coming from my exhaust. I checked it out...I even hit the cat lightly with a hammer...but nothing rattled. I took it to my muffler shop and they couldn't find a place where metal might be hitting each a heat shield or anything...but he suggested that maybe my CAT was going bad. The thing is only 4 years old...but maybe somebody can help.
It seems to be that it is loudest when the car is on cold start. BUT when it heats up, and I rev it a doesn't rattle....
I took some audio clips so that you can hear what I hear.

CLIP 1-I started the car and you can hear me walk around to the rear of the vehicle just behind the tips, then walk back to the side and stick the recorder under the car. (

CLIP 2-This was after the car warmed up...when I got to work...about half an hour later=barely any rattle. (

CLIP 3-This was after I got out of had been sitting for about 4 hours and fifteen minutes. Rattle back b/c car was on cold start. (

Does anybody know what is going on????


10-27-2004, 10:58 AM the way...I have SLP full catback

10-27-2004, 11:12 AM
I had a rattle similar to that in my old Z-24. It turns out it was the material inside the cat was cracked and rattling around. It didn't sound exactly like that, but pretty similar.

10-27-2004, 11:39 AM
That sounds like a heatshield contacting your exhaust pipe. The heat shield that goes around the driver's side of the gas tank will contact the exhaust very easily. Even if it doesn't look like its touching.

You need to get underneath the car and bend that shield up as close to the fuel tank and body as you can.

10-27-2004, 01:30 PM
Been there done that...I already checked the heat shields and so did my muffler shop. I bent a couple back and that did not cure the problem, not to mention that a shield will not account for the fact that it doesn't happen when the car warms up. I'm thinking cat...which means i'm gonna be buying another one...can anybody find me a partnumber for a magnaflow/carsound cat...or any other good ones that you can think of. I might as well go high flow while i'm at it......

10-27-2004, 08:27 PM

10-27-2004, 09:06 PM
I don't think it's the heat shield. You are getting a fast rattle noise. I don't think the pipe can be hitting the sheild that fast.

Roush GT
10-28-2004, 04:45 AM
mine is doing that.. cat is most likely the culprit

10-28-2004, 04:53 AM
Its definately the Cat, ive had the same problem already on an 02 and guess what its doing it AGAIN.

If your going down the highway and you hit full throttle you can really hear it and as time goes on it will eventually get worse and your exhaust will smell like **** and gas mileage will go to nil.

10-28-2004, 07:23 AM
Gas mileage is definately terrible

Climbed under there this morning on cold start and put my ear up to the cat...its the cat...****...more money to

10-28-2004, 08:18 AM
So what are good aftermarket cats that bolt right up with SLP exhaust?

10-28-2004, 12:18 PM
If you get an aftermarket cat, chances are you're going to make a trip to an exhaust shop so you can get it welded to your piping.

10-28-2004, 01:51 PM
Im thinking of getting the cat put on after the SLP pipes are in.... This way I can put it in and let the shop make welds...

10-28-2004, 02:39 PM
yep definately the car...friend had that problem on his 93 ga

10-28-2004, 05:48 PM
Ok....I'm on my girls screen name...too lazy to switch users.....

I bought a magnaflow cat today at Jeg's...had it intalled at Tuffy muffler...all in all...cost me 180 after taxes.

Car feels like a totally different animal...definately not faster (lack of backpressure) probably slower with my luck...exhaust is much louder. My parents are gonna be ****ed when I come home late at night and wake half the neighborhood up and never even make it over 2500rpms. Oh well....

It's the oval cat....fits in there very nicely...and has a pretty SS mirror finish on it....all I know is that the biznatch better not be rattling tomorrow morning at 6.30 when I leave for work..............

10-28-2004, 10:16 PM
damn dude..thats expensive job..u can get a nice cat on ebay for like 35 bucks and install it for another 30

10-29-2004, 02:49 PM
Oh well...this cat is quite nice...the car is very loud now...obviously got more flow than I did. It definately put a damper on purchasing DHP though...:(

10-29-2004, 03:23 PM
Sounds very similar to the problem I had on my Grand Prix... only mine was far more embarassing.

I'm placing my 50 beans on the cat.

10-29-2004, 09:14 PM
Started up this rattles....only problem is that it sounds like there might me a leak...and when I'm at sounds like the tips are rattling or something..hell if I know...gonna have somebody drive by me in my car so that I can listen....

10-30-2004, 08:00 AM
I have SLP also and have the same rattle. Its not your cat. I cant figure out where its coming from either.