Ugh, I'm having a similar problem...I hate the sound of the exhaust vibrating against the frame...between that and the slight exhaust leak at the manifold it makes it sound like the car is falling apart, or a total clunker. It doesn't do it all the time though. Replaced the entire exhaust and it was fine for awhile but now the back of the muffler is hitting the frame again in that one spot. If only I could find a new exhaust manifold then I'd bother messing with the positioning of the rest of the exhaust again too.

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1976 240D "Katja"