A very hard "thump" comes from the rear end on upshifts when under less than full power. I was told by two different mechanics that it was due to a vacuum leak, and one determined that the leak was inside the dash area. The independent shop advised me that no real harm was occuring (fluid in the torque converter), but the dealer's mechanic stated otherwise. This car has over 300,000 miles on it and other the above problem runs fine, see no reason why it won't hit 500,000. Would really like to hear from another source on whether I should go through the expense of a dash removal to fix this problem, or if it is a relatively benigh situation.

Chuck Z.

A vacuum sounds like a very possible cause. The leak however could be anywhere in the engine compartment or behind the dash or even behind one of the seats. Be sure they know exactly where the leak is before proceeding. I would have it repaired soon. Who knows what damage it is doing to your transmission? Benzmac

DIESEL ENGINES PRODUCE A GREAT DEAL OF TORQUE, THIS CAUSES WEAR IN THE RUBBER BUSHINGS IN THE MULTI-LINK SUSPENSION.
IT IS VERY COMMON FOR WEAR IN THESE BUSHINGS TO CAUSE LOOSENESS & NOISES AT THE REAR OF THIS MODEL. ALSO THE RUBBER BUSHINGS AT THE REAR OF THE REAR END FAIL & CAUSE NOISES.

Might this not be caused by general wear and tear in the drivetrain? I would check the driveshaft rubber couplings, driveshaft spline and the free play in the diff. pinion. Also check the diff mounting bolts and rubber bushes, and the rear subframe mounts.