I had a like problem on our 98 C230. Shortcut; start with the tires! Our 202 body is a lot more sensitive to tire noise than our 300E. Even tires that have no visible cups, scallops, irregular wear, and with about 50% of tread left sounded like a worsening rear differential problem to us (and to the dealer).

Coincidentally, we decided to put larger rims and tires on the car before dealing with the noise 'problem' the dealer couldn't pin down under warranty (they said it was there, but they couldn't identify the source well enough to justify rebuilding/replacing the diff.). As soon as the new tires got on the car, the noise went away. The factory Goodyears didn't have any obvious problems according to the tire shop, and still had half the tread left, but roared like a bear when on our car.

We have had 3 sets of tires on this car, and while none were as bad as the Goodyears, all of them seemed to develop a loud road noise in the rear seat area of the car at about 60-80% wear, despite religious tire rotation and spin balancing of wheels on the car.

This may not be your problem area, but doesn't hurt to check it out!

__________________
John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E