Can you find out what fluids they used when they did the fluid changes? Specific viscosities, types, and brand. Is it possible to tell if the noise is louder from the front or rear and left or right side of the vehicle? You may need a second person in the car to help identify a general area the sound is loudest.

I bought all the stuff. The garage did only the job - made many X5s... Done in less than 300km.

Fluid was FEBI ATF / LT71141 with MANN filter kit (filter, gasket, O ring)...

I think the noise is coming right below driver seat under the car - transferbox - but the sound doesn´t seem it comes from some lubricated area inside?

What about the differentials (front/center/rear)? If the noise is only present if the front wheels are spinning, then that eliminates the transmission as a possible source (for now).

Centre "diff" is transferbox am I correct? Rear diff oil changed aswell... Front diff not yet, but the noise is really under my seat from outside...

yes, center differential AKA transfer case. Maybe not enough or too much oil in transfer case? And what oil was put in the transfer case?

Changed today. It was low and dirty, but no change... Castrol DexronIII.

Have you pulled the wheels off, checked the abs sensor wheel, the dust boots on the constant velocity joints on the front axles, and other rotating parts?

That's a sound I haven't heard before. I mean it could be a wheel bearing, but I've never heard one that loud before when moving that slowly.

Going to garage again today so will take the wheels off and check.

Wasted 2 hours in garage. Checked everything that moves and all fine. I've asked 3 times my mechanic if there is right amount of oil in the gearbox and received 3 answers that the sounds doesn't have anything with gearbox. I'll just leave it and use it. Maybe it will get worse or dissapears. Don't know which way to go to find out. I'm tired. :dunno:

I was thinking center bearing on rear driveshaft, except it doesn't make noise if the front wheels aren't turning?