My rebuilt rear diff is on the way back and I will install it soon, hope she doesnt whine. The LSD will be working again, but if its ring and pinion gears have enough of a worn spot in them like my current rear diff, I will get to continue to listen to the whine. At least the LSD will work, I'm keeping my fingers crossed. My rebuild guy seemed to think the gears looked good.
The heavier oil and sound proofing only masks the noise so much and almost not at all with the windows down.
As weird as it sounds, my old German mechanic, who seems to know everything about MB and I trust, got in the trunk of my car, closed the lid and told me to drive. i did. We went for at least 5-10 minutes with him back there in the trunk while I was driving though town. He was listening for the noise. I has a clunk and a whine. HE not only pinpointed the location and parts that were making the noise, but also knew which side. It can be very hard to do by yourself from the driver's seat. The noise can "move" depending on what it is echoing off of and what not. Maybe you can find a trusting pal to ride the trunk. It will make sure you dont replace wheel bearings on a whim. Sometimes the bearings are dry and the heat created from movement can lubricate them and they can stop some of the noice after a few miles, But if that is the case, they still need replaced, they will self destruct eventually. Good luck.

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red