I been hearing humming noise from the rear of the car. Tires are getting old, they are at 5/32 and 4/32 so I assumed that just tire noise. A buddy was in the car as we went to lunch and he mentioned the noise as being abnormal. Now I cannot "unhear" the noise. It becomes audible after 30mph even with accelerator not pressed. It's like a humming noise with a little bit of "warble" in it. No scraping or metal sounds, which is why I though tit was tire noise.

I bought it into a local repair shop -- not Mercedes specialized, just normal automotive shop.
They put a stethoscope on it and said noise was coming from the rear Diff. I paid them to replace the rear differential fluid, with no change. They said the fluid did not have any metal flakes in it.

I took to to the MB dealer where I purchase the car. They did indeed confirm the noise along with some others issues -- which I will post a separate thread on. Here is the video diagnostic: https://drive.google.com/file/d/1EBI...ew?usp=sharing (55 second mark)

Car is about 10 years old and 62K miles on it -- I don't track it or race it at all. After first set of tires that were so expensive, I stopped pushing the car. I drive it casually 16 miles a day round trip for work.

Some questions:
1) Is this typical for this mileage, I didn't find a lot of instances of this on this forum and Grok said it is not typical
2) Dealer quoted $7,800 for replacement. A transmission specialist quoted $4,300 for it with MB ordered part. I'm assuming that $3,500 difference is worth going to a transmission specialist even if they are not MB specialist? They said a transmission is a transmission.

Thanks for the thoughts!

A transmission shop has rebuilt thousands of rear diff pinion bearings.

It's a simple job for pros with 4 new bearings pressed in.

Use a $30 neodymium drain plug to capture glittery contaminants to stop repeat...