Strange whirring/grinding noise

[florissantti]

I have an 83 300d and all of a sudden, JUST before 250,000 miles, it started making this bizarre noise. At first I thought something was rubbing on the tire but I've inspected them and that does not seem to be the case.

Here are the facts:

Unrelated to the engine and engine speed.
Unrelated to which gear the transmission is in.
Unrelated to whether or not I'm applying the brakes or steering.
Completely dependent upon my speed; the faster I go the faster the noise goes.
It kinda seems like the noise goes one full cycle when the tires go around at least a few times.
It seems to be coming from the rear of the car.


The noise itself is sort of a combination of the sound you get when you spin and electric motor when it is not powered and something rubbing and kinda squeaking. It's a pretty serious (sounding), very noticeable noise.

Also, and I haven't checked this out fully, but it seems like it makes noise more at slow speeds if you have just decelerated from a faster speed. That is, it's hard to notice at 5mph if you just got there from zero as opposed to having just slowed down from 60.

Any ideas? I'm pretty worried about this.

[rrgrassi]

Check the center driveshaft carrier bearing and bushing.

Also check the diff oil level

[pawoSD]

Could also be a CV axle failing, check the boots and make sure they are not torn....

[Diesel911]

What area of the car was the sound comming from.

Bad Wheel Bearings can also make a grinding sound.

[florissantti]

Ok, none of that sounds good and that is what I expected. I'm pretty sure that it's not the CV as I've had those go out and that's not really what this sounds like.

The rear diff. is covered in fluid and so my bet is that it's low on fluid. How much of a pain is it to fill that up? Is it likely it's now toast after having been run low on fluid?

I'm hoping that it'll be fixed once fluid is put in.

[rrgrassi]

You will need to check the fluid. Remove the fill plug before you remove the drain plug.

If there are metal shaving, thatis not good.

Do not settle on just the rear diff. Check the entire drive line.

[barry123400]

Putting the rear of the car up on jackstands and powering up may indicate a location if you are having difficulty isolating it. Be careful of course. I suspect a rear wheel bearing incidently.

Yet you never know for sure till you at least localise the noise. As you turn the rear tire on each side manually first put your finger on the backing plate or nearby. You may feel the roughness in the bearing telegraphed to your finger.

This is a way occasionallty to feel for a rough bearing. Also compare the amount of play on each side by statically trying to move each wheel in and out plus prying in opposite directions on the top and bottom of the wheel at the same time. . One side very wobbaly loose in comparison to the other side is also an indicator.