From your description it would seem to be drivetrain orientated. Am not familiar with the typical problems that occur with your model but would suggest looking at driveshaft flex disks, or maybe a motor or transmission mount.

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Terry Allison
N. Calif. & Boca Chica, Panama

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