I changed the flex discs and center support today on my buddies 85 300sd. It had a bad vibration under load but was smooth as silk and silent other than that. I got it back together and the vibration is gone 100% but now I have this strange resonance at 1,000 rpm and again at 2,000 rpm. It does it sitting still or moving. It feels as if the exhaust is making contact with the body but it isn't. Anyone experienced this? I have to figure it out. The car is noisy and rough now.

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