Sounds like pebbles rattling in the exhaust

[TazMan]

Hello all. Earlier this week I went to start my car, and I noticed a noise that sounded like it was coming from underneath the car. The best way I can describe it is that it sounds like pebbles or something rattling around in the catalytic converter. It only lasted a few seconds and eventually went away. The next couple of days, was the same thing but today when I started it, it sounded alot worse, and didn't go away so quickly. It didn't stop till I started driving. I checked the exhaust hoping to find something loose or maybe a cover on the cat rattling around but I found nothing and am starting to fear the worst. It usually only happens on the first start of the day, however today I only started the car once. The car runs perfect otherwise. Anybody have any ideas what it might be?

[sil]

cat conv shield has come loose ?

[TazMan]

Thats what I thought at first two but I didn't find one on it at all. Also, I figured if it were the cat cover it would always make the noise, but it starts off very loud when I first start the car and slowly gets quieter till the car gets hot. Then it's usually gone. I haven't actually had a chance to lift the car yet and check though. I just crawled underneath and felt around. I'll have to do that this weekend. I'm just worried it might be a bearing or something since I have a 3400 top end waiting to be put on this motor and I don't have a hoist or a garage to pull the block if it needs to be changed.

[IsaacHayes]

Yeah my beretta doesn't have a shield over the cat, just the one that attaches under the car going down from the downpipe back.

I'd say your cat has got a hairball! lol It's breaking apart. Time for a new one or hollow it out and put a pipe through it.

[TazMan]

I'd say your cat has got a hairball! lol It's breaking apart. Time for a new one or hollow it out and put a pipe through it.

Wow, am I relieved to hear you say that. I didn't know they just broke apart like that. The pipe would be great as I am very broke right now, but I'm already 2 weeks over due for inspection. Looks like I'm gonna have to put off the top end swap a little longer, but it's certainly better than what I thought was wrong. Thanx again for the great info!

[IsaacHayes]

Well if the sound is coming from the cat, it's likely the cat and not your motor.

They are ceramic or some sort of material in there like that. You could take the exhaust off behind the cat, and knock out all the stuff, start the car and blow it all out. Then re attach your exhaust but if you want best flow characteristics it's best to take the whole cat off and weld a straight through pipe inside it so the exhaust doesn't expand and then slow down when it enters the cat area. But that's getting picky.

Just hollowing it out will do you just fine and free up some power. If the inspections just look to see if you have one on (like here) and don't test emissions, you'll pass fine.