My 99 ML320 has started making a wurring noise in the rear end that sounds like I have tires with very aggressive thread (which I don't). My SUV has 66,000 miles on it. Mechanics at the tire store traced the sound down to the area of the rear differential. Anyone have experience with this situation? Sounds expensive!

With a 99 could be the bearing on the drive shaft. Also but unlikely could be a problem with either the rear differential or the transfer case. The latter was more common with the 98's

it is more likely it is a bearing in the transfer case. Yes it can get very expensive.

the bearing on my driveshaft needs to be changed, 530 bucks, at the dealer now