Rear end humm from W126 560SEL.
 

I'm currently looking in buying a 560SEL and finally spotted one to my tastes. The car is perfect overall but the owner states that there is a mild "humm" noise coming from the rear. The car has 137k miles The noise is constant at all speeds and is very minimal. He also stated that it will need a axle bearing kit to rid of that noise. Could that kit rid of the noise or could it also possibly be coming from the rear end differntial in need of fluid?? The axle bearing kit as the owner stated was about $42 and under 2hrs labor. Can anyone please give me some info on this issue before I go to my mechanic???

I have had/sold my 380SEL and 420SEL which are W126 models and I never experienced that "humm" noise. My 380SEL had 52k miles and my 420SEL had 143k miles.