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 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