Knowledge of the operational loads is very useful in diagnostic process of mechanical structures and to simulate the response under working condition. In many cases, dynamic forces are not directly measurable and need to be identified using inverse solution method. In the present work presented are methods of identification of uncorrelated operational forces based on orthogonal decomposition of response PSD matrix. In this purpose were used methods based on eigen- and singular value decomposition of response PSD matrix and new method based on regularization. Except methods in frequency domain were used methods in time domain (ICA - Independent Component Analysis) for identification statistically independent and principal component. The method was used to identify the number of sources of the exciting forces acting during the work of a real mechanical system - machine for compostable organic materials processing.