A common assumption about fluid power systems is that the outlet pressure ripple is a primary source for air-borne noise. Fluid pressure fluctuations are caused by flow ripples generated by positive displacement units that are the prime power movers in these systems. The present research aims to leverage previous efforts in the topic of noise generation in hydrostatic units, formulating a method to predict air-borne noise for a particular reference machine. A numerical model has been developed to gain knowledge on the mechanisms of noise generation in external gear machines. The simulated noise sources are then applied to the structure in order to predict the propagation of noise to the surroundings. Also, experimental activity based on an innovative method of interpretation of noise measurements is also accomplished in order to better characterize the dependency between fluid-borne noise and air-borne noise. Measurements are made of total sound power level as well as sound pressure level at representative points to better understand the acoustic performance of external gear machines at a wide variety of operating conditions.