Lenkung: Noise when turning steering wheel

[Beumers]

Hi all.
Sinse a while, sometimes there is a noise when I turn the steeringwheel. Left and right. Sometime there is also a resistance feld in the wheel. Little short knocks. I checked the ATF level but that seems to be allright. ( depress brake pedal 20 times. Level is almost at the rim/top. According to the Bentleys manual it should be 2,5 cm under the rim. In my knowledge it can't be to mutch. You don't want to spill it but oké.)
I thought the noise is related to air trapped in the system. Turning the wheel several times to the left and the right should get the air out. Still after a while the noise comes back. There is some leakage in one of the electrical sensors but it's not that bad. Fluid level is oke as stated above. The system also provides pressure to the hydraulic brake booster. No problem in brake performance.
Someone has any experiance with this item.

No need to reply in English. Henk.