We report on experimental and theoretical results on thermopower. This contributes to the old-standing problem that in disordered metals the thermopower very often shows at elevated temperatures the opposite sign in comparison to the Hall coefficient. Liquid and amorphous materials show characteristic low-lying anomalies in their phonon dispersion at scattering vectors K where the static structure factor shows a peak. Since in many glassy metals 2kF is located at the same K-value, subsequently, the electrons may suffer strong elastic umklapp-scattering effects with the static structure and as well a strong inelastic umklapp scattering with the low-lying phonon anomalies. Versus temperature the inelastic part changes drastically and the thermopower switches from a negative to a positive value.