Implications of the violation of adiabatic conditions for sound propagation in a gas layer adjacent to a phase interface is considered. It is shown that, for Knudsen numbers exceeding 0.01 (circular frequency ω≈107-109 Hz under normal conditions), viscosity waves and temperature waves become a significant radiation mechanism of surface acoustic waves (SAW). Experimental dependencies of the SAW attenuation coefficient on frequency, the molecular weight of the gas, and pressure are described for the first time.