Wondering if anyone might know what this is:

Sometimes when I close my door, I can hear some kind of metal rattling under the car. It doesn't happen all the time. I don't have much knowledge about cars, so I was wondering if anyone could help. Thanks in advance.

 

If it's really coming from under the car, the first thing that came to my mind is the catalytic converter may be broken inside. Often when the cells break, they rattle around inside the cat. It could be something else, too. Do you know where the sound is coming from exactly? Can you hear the rattle over bumpy roads? Can you hear the rattle with the engine at idle? Can the rattle be coming from within that door (is it just when you close the one door)?

 

It's hard to tell exactly where. I really can't hear anything from inside the car, it's usually after I park and close the door from the outside. So, no noise during idle or over bumby roads. I'm pretty sure the rattling is not from the door.

 

Is it the same on both sides? Is it as loud on both sides of the car? If you slam the door on the other side, do you hear anything different? Less, more, different noise?

I'm still thinking it may be in the cat; that some of the cells have broken inside the cat and they are rattling as you slam the door.

 

Yeah, I don't think the door really has anything to do with the noise. It is just a means to shake the car I guess. I'll hear the noise if either door is shut. Ok, assuming it is the catalytic converter, is this a big problem?

 

Yeah, but first double check it by getting under the car and banging on it with your hand. Don't bang on it while it's still hot (of course) and don't bang on it with anything else, like a hammer, because then you could break the cells even if they are OK. If you get the same noise, then you know it's time to replace the cat.

 

Thanks for you help by the way, but one more thing. I did just get a smog check, and if the cat converter is busted I doubt it would have passed the smog check right?

 

Did you hear the rattle before the smog check?
It is possible that the cells could be damaged and still be able to pass a smog test, though. Rare, but possible.

 

what state do you live in it could pass the old test quiet possible but probly not the new ones that they got in CA and MA

 

Hmm, ok. Well anyways thanks for the help, I will look into this cat converter. Yeah I live in CA..
The weird thing is that it doesn't happen all the time, only on occasion, but I can't figure out any pattern to it.
Also, I don't remember hearing it before the smog check.