Nezar--what color is the fluid? Will you be DIY? Do you know that the replacement part is in good shape? Getting stiffer after running for some time could be getting a joint hot if they are not good and cause binding. No Clicking noise when you turn the wheel?

DT Man- FYI-there are many sources for a clunk that sounds like it is in the steering wheel. I would start by spraying WD40 on all the steering wheel Universal joints--see schematic in earlier post. How many miles on the current front suspension?

AKE 53--If you can make it click in park with engine running at different RPMs have someone turn the wheel back and forth while you put something metal or a stethoscope on the steering rack and to your ear. If the noise is louder than other metal steering parts close by that will tell you it is probably in the steering rack. If that is not the source try other steering parts though clicking is a common symtom of a steering rack problem. Either way click or no click test possible, I would then change the fluid especially if it hasn't been changed for a long time or is brown, should be red.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas