drlyncher

When the engine is running, but the vehicle is not moving, a rattle heard from beneath the vehicle could indicate that one of the exhaust catalytic converters has failed. The substrate (the internal part of the catalyst that reduces emissions) can loosen and bounce around inside the canister section of the exhaust pipe—the defective unit will need to be replaced. If this problem is ignored, the substrate can break down and reduce to a size that plugs the outlet pipe, which will cause a sudden loss in power.

I copied the above from another site....think I may have this problem - has anybody had this problem before and how much would it cost to fix?

dlbehrns

jack up the car or put it on a lift and bang on the secondary ones first. or, maybe you have a heat shield loose.
here's a pic of what they look like but not necessarily what you need to spend
http://www.catalyticconverterwarehou...VERTER&mode=PA

http://www.randomtechnology.com/index.html has as good a product(I'm told) as you can find. call them and they will give you an application for your car. you will either have a custom shop cut out the old ones and weld in the new or cut them out yourself and use clamps unless you are a welder of course. http://www.amazon.com/gp/product/B0006HLFCY. I have never used the clamps but some say they leak. COMMENTS?

blckhawk84

I have a 2001 Clk 320 and there is a grinding noise that the vehicle makes when I accelerate out of first gear or accelerate in reverse. The catalytic converter was replaced by Mercedes last year (under warranty). The grinding noise it makes now is different than the grinding noise from the faulty catalytic converter. I took the vehicle to Mercedes of Long Beach for an oil change and they told me they wanted an extra $375 to search for the source. Anyone else have/had the same problem or might have a suggestion as to what is causing this noise?