[en] On TRIGA Mark II reactor measurements and analyses of some stochastic signals were performed to determine their reference spectra in the frequency band from 0.01 Hz to 100 Hz. Autopower spectra of neutron flux fluctuations were computed for full power and for 50 KW and 5 KW at different cooling conditions. The spectra show a significant resonance at the frequency of 2.3 Hz which dependence on the state of the cooling system. To determine the cause of the resonance vibrations of coolant water inlet pipe, ionization chamber and control rod were also investigated. Reference power spectra of these vibrations were found and only a slight correlation between the ionization chamber and control rod vibrations and the resonance were established. Since control rod vibration are most probable cause of the resonance preliminary measurements of control rod vibrations should be improved to prove this hypothesis