Relaxation of single defects in a nanometer-sized resonator is observed by coupling surface acoustic waves to freely suspended beam. The surface waves act on the resonator as driving forces being able to modify the internal friction in the beam. In analogy to classical experiments on internal friction in macroscopic samples, we Perform frequency, amplitude, and temperature-dependent experiments on the nano resonator and find a scenario which is consistent with the observation of single-defect relaxation.