What is this noise? diff, driveshaft, bearing, it's driving me crazy...
 

I'm helping a buddy of mine, between us, we have 3 W210 E300's. (2 99's and 1 98)

The oldest car, 150K, has picked up a whirring almost grinding type of noise, that starts at about 30 MPH.... I immediatly thought tire, changed tires.. no joy. So... we jacked it up.. scratched our heads, replaced the brakes.... still has the noise. I'm actually ASE certified, so I"m embarased at this point... now we run it with both rear wheels in the air... no noise. Closer inspection, we figure it's a right rear wheel bearing. after all... that hub is warmer than the other side, and that is the side the noise seems to come from. After replacing the wheel bearing... the noise is the same. So... now we're running out of choices. What could this noise be.

It sounds like a tire.. but not wop, wop... it's sort of whirl whirl, with a little grinding type of noise with it.

My latest thoughts are rear diff. How often do they fail on W210's?

What are your thoughts?

We're going to change the diff fluid, just to look at it, but we're not looking forward to a diff failure. This oldest girl in the fleet has been tough on us the past year, and especially the past few days.

Who thinks they know what this rotating noise is?



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Same Noise, @ Same Speeds
 

I encountered same thing, same sound. New tires, pulled driveshaft checked center carrier bearing, mounts, & flex disks, No improvement.
Changed fluid in rear, Nothing. Ran with rear on stands, Nothing. Finally went to the dealer and had the rear wheel bearing changed.
Not saying you changed the wrong side, but that was it for me. Drove me nuts, I almost felt good about the dealer repair invoice.

Good Luck.

Jack up rear of car. Grab rear wheel at 12 and 6 o'clock position and rock to see if there is any play in bearing. There should be no noticeable movement if bearing is good. You check fronts the same way(Except that you jack up front of car.)

Generally, if the diff is the issue, the noise will change depending on load. It will likely get quieter on heavy loading and the noise will increase on cruise or at light loads. While this is not definitive, if you notice this behavior, then I'd lean toward the diff as the culprit.

The fact that you get nothing when the rear end is in the air would probably rule the diff out..........the load is minimal and it should be making a decent racket.

The fact that the noise disappears when the wheel bearings are unloaded also tends to point you in that direction.