When I'm driving on highway above 40MPH, when the car is accelerating or going up a slight hill, I hear a humming noise. I can feel a slight vibration in the car, it stops as soon as the drive train is not under a load (level road). And then returns when drive train is under a load again. Im assuming a u-joint or flex joint, whatever MB calls them. Car has 119,000 miles on it and they have never been changed as far as I know. ( Im 2nd owner).
Are there any other things that could cause this? What about torque converter? Transmission shifts good and is nice and tight.
thanks ron

 

Axle shaft, differential bearing.
It may also be bad engine/transmission mounts altering drive line orientation under load..

roy@pelicanparts.com


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Ok, so I jacked up the car and got under it for the first time and there are no U-joints on this vehicle. So, that's definitely not the problem. I checked the CV joints in the rear and they look and seem to be fine, no leaks and boots are sealed. Rear diff has plenty of oil. So Im not sure what is causing the noise. Im going to drive it until something breaks, then Ill know for sure.
thanks r

 

Is this a base or 4matic model ?
The VIN# would help with isolating possible issues.

FYI: The drive shaft has one U-joint in the center, though it is a rare failure.

Waiting for a terminal failure is a bad idea with a 1999 E320 Mercedes Benz, the repair cost can easily top $7,000.00 USD.



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Roy, thanks for the reply back. Today we put the car up on the lift and looked around under the car. We checked an changed the diff oil, it looked to be untouched since it was filled at factory, all cv joints looked good, drive shaft looked good. I think we may have found the problem. One rear tire was worn badly, so we checked the alignment and it was off on one side really bad. Im putting new tires on next week. So hope this was the problem.
thanks for the input.
Ron