While we had the car up on stands, I span the rear wheels...
There is a metalic "TING" noise when the rear wheels are spun back and forth.
I traced the noise to the main driveshaft.
There is some play in the forward rubber drive coupling...
I assume any visible movement in that joint is bad?
But the Ting noise was coming from rearward of that.... up above the exhaust/exhaust shield where I cannot see. If I grasped the driveshaft at the front and twisted the rearward section, I could not feel any play in the driveshaft, but if I let the forward section loose and twisted the rear section back and forth I could hear it going TING everytime I reversed direction...
I hope that makes sense!

I know from studying the Haynes manual that there is a center coupling/support/bearing there....
Is it worth pulling the exhaust off to look?

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2009 Mercedes ML320 Bluetec