93 190E 2.6 Drivetrain Whine

My 93 190E has a drivetrain whine coming from the rear of the car. I've had the differential replaced twice [about 15 months ago] with M-B rebuilts - once by an independent local shop specializing in M-Bs, and once by the dealer. The first swap-out only had a minor affect on the noise. The second swap-out, at the dealer, eliminated the 'always there' component of the drivetrain noise, but did not eliminate the noise described below. Front flex disc also replaced at same time.
The whine occurs under the following circumstances:
1. At a steady 25-30 MPH when slightly letting up on the throttle. The whine disappears immediately when the throttle is pressed down, even slightly, or when foot is taken off throttle entirely.
2. At about 70MPH, same circumstances as above.
Thanks for your assistance.

[Benzmac]

Two things. These diffs were known for this. Also, I have seen in the rarest occasion, the rear seal in the tranny whine because it was too dry. ( I don't think that this is your problem, but I had to tell you about it.)

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Benzmac:
1981 280GE SWB
1987 16V
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