My dad has a 97 e420 which has an obnoxious rattle coming from under the car, about half way back. He says it has something to do with the catalytic converter, and it is a big, expensive job to fix. It only makes the noise when the car is in gear, not when it is in park. Anyone else experienced this type of problem? Something doesn't seem right to me, but I can't really go under there to check it out because it would seem as if I was second guessing him. Thoughts?

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headrivenoise... listen.