Combined use of low angle high resolution X-ray diffraction, to ascertain film structure, X-ray reflectivity, to obtain film thickness, and surface Brillouin scattering, to determine film acoustic properties, has provided structural and mechanical characterization of thin alloyed gold films, deposited by magnetron sputtering on Si(001) wafers. Although weak, the variation of the elastic constants of Au, as induced by small Cu and Ni contents of the film, has been revealed. The X-ray measurement of both film thickness and density is shown to be crucial.