Many hydrogenated pure metals and industrial alloys with FCC lattices show a distinct internal friction peak above room temperature caused by the thermal desorption of hydrogen. Based on these observations, a new method for studying the hydrogen diffusivity and the interaction of hydrogen with lattice defects is proposed for the temperature range of 250–500 K. The desorption origin of the peak was studied in detail in hydrogen-charged Inconel 600 alloys with different carbon contents. The peak was shown to possess transient and non-relaxation nature. In some cases, a fine structure of the peak caused by hydrogen traps can be observed. A theoretical model of the thermal desorption effects on the losses of mechanical energy, i.e., internal friction, in metals is developed.