The HPGe detector assembly of gamma-ray spectrometer cooled by Stirling cycle cryocooler is under consideration. Modal analysis based on the compiled dynamic model was carried out. The natural frequencies and modes shapes for HPGe detector with relative efficiency 15% mounted by supports made from composite G-Etronax and CESTILENE HD 1000 were calculated by Solidworks simulation. The frequencies of the axial mode are in range of 200-600 Hz where electrical interferences caused by mechanical vibrations (so-called microphone noise) has a large impact on the resolution of spectrometer. It is shown that for cryostat cap the lowest natural frequencies determined by the thickness of input window lay in higher frequency range. The validity of the adopted model was confirmed by the experiments. The calculated natural frequencies of the detector assembly are compared to the harmonics of cryocooler’s vibration. The results obtained are useful to identify the interferences source in electrical circuits of spectrometer at its adjusting.