On my E300 diesel, I went through 3 dampers before discovering partially collapsed motor mounts were the root cause.

Your tensioner is subtly different than my setup but is easy to check the condition of the mounts to rule that out.

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Terry Allison
N. Calif. & Boca Chica, Panama

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