UPDATE 2
Over the past 6 months, both secondary cats began rattling. My original intent was to have them cut out and have aftermarket replacements or straight pipe installed.

Because an empty converter housing is, for all intents and purposes, a straight pipe, earlier this week my tech dropped the exhaust, gutted the secondary cats, and solved the problem (and improved performance).

I should add that the sound of that V8 with no mufflers is simply wonderful; don’t know why MB chose to tune it to be so quiet.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black