Humm from rear end
 

S500 Humm from Rear End
My Car is making a sound as I increase the speed. It is absolutely revolution based. I jacked up the rear end and started the car (you have to remember to turn off the ASR) and the noise seems to be coming from the differential, however it might also be from the drive axels from the diff to the wheels. Anyway, in looking at the differential, I see the drain plug toward the bottom of the differential, however, how do you add anything )assuming I wanted to try and add some Slick 50 gear oil or something like that). Secondly, as I increased the speed, there was a deffinite vibration coming from the right rear portion, but with the wheels off the ground, I thought that might just be a balance think where I might not have had the car leveled.

Thanks

I think you might need a rear axle bearing kit. I'm currently buying a 560SEL with 137k miles and the owner states that there is a mild humming noise that doesnt change with speed. He states the car will need an axle bearing kit for the rear??? I could be wrong but you might need to do this job as well as change/add fluid in the differential