W210 4-matic annoying droning noise from left front
 

My car makes a very annoying droning noise that seems to com from the left front wheel.
When it is warm outside the noise starts after a few miles, when it is colder, it takes up to 10 mls before it starts.

A sample of the noise is in the following link:
http://test2.ergonomie-advies.nl/images/Noise.mp3

1. It is slightly intermittent, sometimes is stops for a few seconds.
2. With microphones under the floor insulation, I detected the loudest noise near the accelerator pedal.
3. Rotating or changing tyres has no effect.
4. The tone does not vary with speed.
5. Changing directions has no effect.
6. It is louder when cruising.
7. On a lift (with all wheels off the ground), there is no noise.
8. I also blocked three wheels so only one wheel is turning, still no noise.
9. I even used axle stands to keep the axels horizontal, still no noise.
10. The rubber parts of the control arm are still somewhat flexible.

Who recognizes this sound?

Rob

I guess you’re saying the noise is constant at different engine speeds and different road speeds?

Just to rule out claimate control, turn off the aC and fan next time it happens.

Which engine do you have?

It is an E280 4-matic (m112) from 2001

It is not the fan or airco compressor.

I hear it even when I put the car in neutral and switch the engine off.

It only makes the noise when driving, not when I put the car on a lift and let the wheels spin.


Rob Pruijt

Is the car stationary or rolling when you do this?

If moving, I'm voting for a front wheel bearing / front differential bearing. ( I didn't listen to the link )

>>I hear it even when I put the car in neutral and switch the engine off.<<

You said the tone doesn't vary with speed, but guessing the volume does?

A bad wheel bearing can drone like the engines of a B29 Flying Fortress (similar to this https://www.youtube.com/watch?v=Tds7Onwz2-U), but it gets louder with speed and is not affected much by temperature.

I only hear it when the car is rolling, with the engine on or off.
It does not change in corners.

I do not hear it when the car is on a lift with the engine on, in drive and wheels spinning.
Also no noise when I blocked all wheels but one and revved the engine up to 30mph (on a lift and repeated for all wheels).

Rob

If it is cold, it starts if I drive 5 to 10 mls with more than 40mph.
When it starts making noise, it does not stop even at lower speeds.
It gets a bit louder with speed but not much.
I measured the temperature of the axles and hubs; they are all in the same range.

If I drive over a speed bump or an uneven road, it often stops for half a second and starts again.

In the last year it gradually got a bit louder, but not much.

It is not loud, but it is very annoying.

Rob

If you can get it on the lift again, when it's warm and noisy, try using a mechanic's stethoscope on each wheel to see if you notice a difference among the wheels or at the diff.

My suspicion is a wheel bearing.

bad engine mounts can cause this noise and vibration. In one case I saw the car had a bad torque converter in the transmission that was causing a rough grinding howling noise as it drove down the road.

Of course I tried to locate the noise with a stethoscope.
Wheel bearings are silent, the diffs make noise but not abnormal.


Rob

Noise from engine mounts of torque converter should disappear if I put the car in neutral and switch the engine off.

Short of getting fancier noise diagnostic equipment (chasssis ears, freq. or spectrum analyzers) I think you’ve gone as far as you can go. It is a wheel or driveline noise, most likely in the left front. Wheel bearings are more likely than diff bearings, because of the loading and environment. The double-row wheel ball bearing doesn’t get louder on turns if it hasn’t failed, it just gets drony as it wears. Because your car is ca. 20 years old anyway, I would replace the wheel bearing.

I agree that replacing the wheel bearings is probably a good idea.
All my previous cars had roller bearings, you notice when the fail.

4-matic parts are hard to get over here, so I try to find what else needs replacing if I take the front suspension apart.

It's my only car and I am to old (60+) to ride my motorbike in winter while waiting for parts.

I did build a chassis noise detector with 6 contact microphones.
It works great for higher frequencies, but not for low frequencies.

I discovered that het contact microphones have a high impedance and the amplifier I used has a low input impedance.
This combination works as a High-pass filter, cutting off al lower frequencies.

I ordered a high input impedance pre-amp from the well know peoples republic in the east (smaller and cheaper than making it myself).

Rob

Rob, are you the guy that used a microphone , a time base synced to an ignition pulse and audio editing software to diagnose an engine valve noise
?

No that's not me.

This construction is actually very simple.
Six cheap guitar microphones connected to a small box with a magnetic top.
This box is connected through a network cable and a six-position switch to an amplifier.
I use a network cable because they are cheap and easy to replace.
The total cost will be around $25 and 2 hours of work.

Rob