Hello All,

First time here,

I have a 118k Mile 2009 E350 recently I've had a noise coming from the rear of the car, this started off very quietly but progressed to a decent volume, I've replaced the rear bearings on both sides, this made the noise ALMOST go away ... for about 2 days then it returned.
Any other ideas of things that I should check?

Details about the noise :

Changes volume and pitch only based on the speed of the car, putting it into neutral whilst at speed makes no difference to noise at all, there's no change as it shifts through the gears. Purely related to speed.
For the level of noise reference, at 70 mph it sounds like you're holding 3500 Rpm or so.
As mentioned I put new wheel bearings on the rear and it came back after only 2 days.

I appreciate any input or suggestions.

Thanks

It's the rear differential. From what I understand, they go on these models because the bearings inside the diff are undersized. Mine went and I had it replaced, noise gone. MB dealer wanted $4600 because they replace the entire diff. I found a guy in NY, Little Bear and he did the job for 1500 by just replacing the bearings within the diff. Here is his website.

https://www.littlebearauto.com/

Look to the left under his specialties and you'll see MB rear Diff.

Good luck

I bet the Original poster is glad that after a year he got some input.

Even if the OP isn't, someone down the road may be happy to have the link provided.