Catalytic converter rattling?

[diogenes]

I had asked a question earlier about a crackling, crunchy rattle:

"When I lift the throttle, as for a gear change (I have an MT), there's a crackle/crunchy sound, kind of like radio static, but it is there whether the radio is on or off. It is most obvious when the engine is cold and at low speed. Putting the throttle back down makes it go away instantly."

I thought it might be a vacuum leak or leaves on the intake screen, but it is still hanging around, despite cleaning leaves out, so now I wonder if is related to the cat. I hear the sound near the center of the dash, and the cat and its heat shields seem to be located near there in the engine compartment.

Anyone dealt with this? Is it just an annoyance, or does it signal that the catalytic converter's core might be degrading and coming loose?

Thanks.

 

[diogenes]

BTW, its a 2006 Mazda5 Touring with about 39,000 miles.

 

[mazdadude]

So it only makes the sound when under load, and not when revving in neutral?

Maybe try popping the hood open, leave the parking brake on hard, and try letting the clutch out a little till it just starts grabbing, try 1st and reverse, do this while having somebody else stand to the side of the car at the fender (please stand to the side of the car and not in front of, we don't need any more Darwin Award winners), and watch/listen for your noise.

 

[flcruising]

It very well could be the catalytic converter. I had an S10 pickup that had the converter break apart, and that thing rattled like rocks in a tin can. I'd take it to a muffler shop, they'll tell if that's it or not real easily.

 

[fkong777]

you can nail down if it is the cat by lightly knocking on the cat with a wrench or a hammer. if the cat broke up inside it will rattle.