1999 Mercedes Benz 430e

Noises problem
1999 Mercedes Benz 430e V8 Front Wheel Drive Automatic 170000 miles

I am told that I have 2 catalytic converters. If one goes out, does the other go out shortly there after? During a diagnostic test, can you tell which converter is bad or is it a guessing game.

Car making noise, diagnositc exam was done, and it was advised that the right converter was bad and needed to be replaced. 6 months after the diagnositc exam I had the repairs. The evening after the repairs, I noticed the same noise. Took vehicle back to the repair shop and was told that the other converter was out and needed to be replaced. Was also told that during the initial diagnositc exam (6m prior ), they could not tell
that the other converter was bad?

Is any of this true?
September 20, 2009.

If they run a 5 gas analysis test it will show up if its defective

Sep 20, 2009.