Steering becomes difficult after 30km, accompanied by a heavy feeling and creaking sounds

Hi everyone..
Recently, I've noticed that the steering in my Golf 3 TDI (built in 08-94) seems to be getting a little heavier after driving for about 30 kilometers. Mileage: 256,000 km
and recently, new Uniroyal 540 tires (the new series) were installed.
When turning with a warm engine after driving for 20-30 km, a grinding noise can be heard, especially when turning to the right. Could it be the strut mounts?
'Or does anyone have any ideas where to look? The power steering pump is tight and dry, and the belt is in good condition.' The servo motor is positioned exactly between the minimum and maximum values.
The funny thing is, this only happens when you've been driving for a short time.
It can't be that the pump is already failing, can it?
and if I have to replace the pump, what type should I get? There are so many different types...
'One person says that the fuel pump from a 3-series GTI would fit. Please help!'