about 6 months ago i put on a downpipe and high flow cat, and i had a little rattle on the lower crossbar.

after a while it started rattling a lot more, i'd say for the past 2 or 3 months. i just thought it was hitting the ACD so i never really looked at it, it didn't bother me too much, but now it does.

so i went under and found that it was rattling from the cat, and there is nothing the cat is hitting. has anyone ever had a problem with the catalyst inside of the cat getting loose and rattling? i think thats what it is...

 

I had the same rattle.......it was hitting the ACD.......so i modified the DP alittle by banging it in somewhat. NOw i have no rattle. Also did u secure the harness for the O2 wire?

 

make sure the o2 sensor isnt rubbing the undercarriage.

 

its definitly not the ACD, its coming from the cat

i glanced at it and i am pretty sure it isnt hitting, but it might be there. i did do the o2 cheater with the spark plug non-foulers, so its possible. i'll check soon

 

I had the same rattle and it was driving me crazy. It would only happen every so often and mostly after the car had warmed up for a bit and it was just idling. You could also only hear it from inside the car which was weird. I had checked everywhere and it was not touching anything. When I finally removed my hfc to install my resonated test pipe I discovered the catalyst had broken free from the housing. You would shake it and it would make a clunk. So yes you could have the same exact problem which is apparently very common with catco items (company which manufactures a lot of catalysts). Catco blames it on rich conditions in the exhaust which cause micro explosions in the cat which beak it catalyst free. I call it a cheap and poor design. I first heard my cat rattle about 4.5 weeks after installation (I was still on the stock rich tune then). I hope this helps.

 

I had the same problem and just as it got to the point of annoying the crap out of me, it stopped. I had just been talking to a local guy and he said he would be able to stop the rattling and a couple of days before I took it to him the noise went away and never came back.

 

Sounds like the exact same rattle I had which led to my catalyst being replaced under warranty. No problems since.

 

*%$@. looks like im getting a test pipe

 

yep. got the test pipe today. the catalyst is shot in the hfc

 

Which hfc did you purchase so I don't purchase the same one. Cats shouldn't dislodge for atleast 75-100k miles.