This thesis is about the study of two important characteristic values of positive-displacement pumps, the source flow ripple, and the source impedance. The first one represents the flow fluctuations generated inside the pump, while the other one the complex ratio between the pressure fluctuation and the flow ripple occurring at the outlet port of the pump when the Norton model is used. The fluctuations of flow rate are inherent to these types of machines due to their working principle. Moreover, they generate pressure fluctuations in the hydraulic circuit at which the pump is connected and consequently leading to fluid-born noises. By knowing the two mentioned features values and the ripple propagation characteristics of the circuit’s components, is possible then to compute the pressure fluctuations through mathematical models.