In this work we present the results of a study on pulse energy noise dynamics of the IBR-2M; the study employs statistical methods of time series (pulse energy) processing and hierarchical cluster analysis. It is shown that the power spectrum changes of the pulse energy fluctuations per cycle (11 days) has a transition region duration of 3 days that takes place after the reactor has reached the nominal power of 2 MW. The power noise is subsequently divided into four stable clusters, with three of which describe the noise transition region. The fourth cluster constitutes a stable structure that does not depend on noise level (amplitude of the power spectrum) or on reactor operation time. The noise transition region is formed by the vibration of the moving reflectors once the reactor has been reached.