2008A64f stiff/stumpy
 

I have a 2008 Audi A6 4f with 210.000 km. Now its getting a little "stiff and stumpy" in the back section when I drive over bumps etc. I also can see when the car have been standing still for many days there can be a little higer back on the left side then on the right side, I can see ca 2-3 cm difference in the distence between the wheel and the karosseri on the 2 sides.

I maybe need to buy new bumperes? What other things can this problem be?