I noticed that when my car is at idle, that it makes this sound like somthing is loose in the catalytic convertor. I went under the car and hit the cat, and sure enough there is something clunking around in there. What could this be? I know that I need a new cat now, but I just want to know what that sound is.

 

That sound is loose material from the convertor bouncing around most likely. Sometimes the "bricks" inside the cat break apart, and thats what you get. Mine is somewhat busted up and rattles at idle, I really need to fix that its annoying!

 

i'd fix that asap. eithe rget rid of the cat(s) or replace it with a high flow. i had one of the cats on my dual cat car snap the brick inside and when i would be going down the track the car would shut off because it was plugging up the pipe. didnt realize it at first because it wasnt rattling. took the cat off and no problems since. also i believe that this may have been a contributing factor in my engine running hot sometimes because it wasnt allowing the exhaust gases to escape freely.

 

Fixed that today with a high flow cat, and while I was messing with the exhaust I added a 3" cat back. These sound SOOOO nice. Sounds just like a Hooker, but it was made at the muffler place.

 

awesome.. congrats.. got any sound clips?..

 

I'll try to get one of my friends to get a sound clip of it. It sounds so bad a$$ . The thing I noticed is that when it gets up high in the RPM range in neutral, and let off, there is a little pop, that only happened once, but I thought it was pretty cool because it makes the car sound like it has headers.

 

sounds like the guts of the cat flopping around


I would say get pipe to bolt into place if you dont have to pass smog
if you do then have it setup so you can unbolt your test pipe and bolt in a cat when smog comes around