The point-contact spectra (the energy dependence of the amplitude of the second harmonic of the modulation current) of contacts of NixNb1−x metallic glasses are measured at audio (3726 Hz) and microwave (9.5 GHz) frequencies. It is established for the first time in rf dynamic experiments that the low-energy spectral feature due the scattering of electrons on two-level systems (TLSs) in the contact is observed at microwave frequencies as well. This is direct evidence of the existence of a fast relaxation process in the contacts, with a characteristic time τ≪10−10s. There is also a small contribution from slower scattering processes. It is found that the videodetection signal contains a component due to a steady-state nonequilibrium occupation of the states of the TLSs under microwave irradiation. The coupling efficiency of the contact with the waveguide and rf receiver is estimated to be 5–7%. A slight minimum of the resistance at zero voltage observed for some of the contacts is attributed to superconducting fluctuations of the order parameter at a temperature T∼2.3Tc.

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