A common problem when operating heavy hydraulic machines consists in low-frequency resonance phenomena that significantly limit the bandwidth of the closed loop position control. The interest in this topic is further motivated by the fact that the usage of traditional dynamic models of hydraulic actuators usually leads to the identification of very high-frequency resonances. This paper tries to explain the origin of low-frequency resonances by analysing the kinematic coupling between hydraulic actuators and structural links that can be found in typical hydraulically actuated machines. A novel formula for the identification of such resonance frequencies is derived. A realistic simulation environment is used to identify the resonance frequencies corresponding to different load masses and link lengths. Finally, the identified frequencies are compared to the results obtained using the two formulas, showing the superior accuracy of the newly proposed approach with respect to the traditional one.