Your profile doesnt say what kind of car you have and the post only states E class?

The "rocks in a tin can" bit could certainly describe a failing cat. At some point the CEL should come on.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)