When I have the windows down on my 2000 e320, I can hear the exhaust system making an odd pipe rattling noise. It's not the exhaust hitting anything, rather it's sounds like a exhaust gas going through a hollow pipe. This is hard to describe - it's most noticeable at lower engine speed. I guess it sounds a little like there's an unusual exhaust leak coming from the major clamp just under the front seats, but I've checked and can't find anything wrong (no telltail black smoke marks indicating a leak, clamps all tight).

I've worked on cars all my life (as an amateur) and so I'd know the obvious stuff. The sound is tinny sounding, like someone put a cheap exhaust on the car, but the overall sound of the exhaust is not loud like a hole in the muffler.

This is a tough one to describe - wish I could do better.

 

Its most likely one or both of the cats. Thr internal baffles break loose and rattle. Recently changed both on my 01 E320. This sems to be a common problem on several MB models.

 

That could be it, because they seem to rattling now and it's not like the exhaust is loose and hitting the heat shields or anything.

Are there more than one muffler? If so, is there any method to identifying which one is bad, since it's internal baffling.

 

On mine, one was changed and the noise lessened but was still there and they changed the other one. Noise abated. Believe that if you put the car on a lift and rap on the cat with a rubber mallet you can tell if its the one. Al I have heard about required both cats to be changed. My 01 E320 4matic has dual cats and one muffler plus a resonator. mine was done under warranty

 

Thanks, unfortunately my warranty just expired.

 

It may still be covered under the emmission warranty or, your dealer may "goodwill" it as its a known problem

 

Good idea. Thanks a lot for your help.

 

Under some law catalitic converters are now covered by an 8 year 80k mile warranty, your dealer should do it under warranty.
Check your manual also, they probably mention that warranty as well.

It does sound like the cats, my car did the same and that's what it was.

 

Thanks Pocholin, I'm checking with MB.

 

Sorry to bring this back.....

Hello everyone....(1st post )

I have the same car 2000 E320 and just experienced this same issue.
Rattling noise, especially when the exhaust is still cold and the rattles seems to go away after the car fully warms up.

My car is now 12 yrs old and under 80k miles

Did the the noise go away after replacing the CATS?

Also where is a good place/Price to get new cats?
Do i have to use OEM or can i just go to a local muffler shop?

Thank you

 

Yes the noise went away. If it's a metal rattling sound, it very likely the converter. I can't help you on best price.