Moving impurity particle causing back flow in a background Bose- or Fermi liquid at T = 0 is treated as a weak inhomogeneity applying the inhomogenious HNC-theory. The Euler-Lagrange equation for the density fluctuation is simple but non-linear. In the case of charged impurity in electron gas the equation is solved in closed form using uniform limit approximation. This already goes beyond the conventional linear responce theory of Friedel oscillations. For the impurity in He-liquids the present theory can be applied to calculate the quasiparticle effective mass and correction terms to the effective mass approximation.