lizem, as I am sure you are aware there is nothing to see when you look under your S430, but you should be able to detect the source of the rattle. If it's the catalytic converter on the driver's side, recommend buying a new assembly from a MB dealer and installing it yourself. Should be a simple bolt-up if it's like our 1998 E320. There is an Oxygen sensor before and after the catalytic converter.

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Fred Hoelzle