The cat may have been damaged during shipping, during installation, who knows? It could just be a very cheap, crap-built aftermarket cat.

If the rattle isn't too bad, you can also try crimping the cat slightly with a large set of pliers or a C-clamp. That can help get rid of the rattle for a while. Emissions and performance are a whole other issue though.

If you plan on keeping the car and want to keep it running well, I'd bite the bullet and purchase an MB (OE) cat.

__________________
Chris
2007 E550 4Matic - 61,000 Km - Iridium Silver, black leather, Sport package, Premium 2 package
2007 GL450 4Matic - 62,000 Km - Obsidian Black Metallic, black leather, all options
1998 E430 - sold
1989 300E - 333,000 Km - sold
1977 280E - sold
1971 250 - retired

"And a frign hat. They gave me a hat at the annual benefits meeting. I said. how does this benefit me. I dont have anything from the company.. So they gave me a hat." - TheDon