The evaluation of the noise performance of hydraulic pumps is a key aspect for manufacturers as the pump often represents one of the main noise sources in hydraulic systems on end users applications. Although sound power tests are the most accurate measurement method for the acoustical characterization of a source, study relies on a more practical and fast approach based on a series of measurements of sound pressure levels at five measurement points around the pump to compare different designs. All tests were performed in the laboratories of the CNR-STEMS research institute in Ferrara, in a quiet environment using a specific test rig which physically isolates the pump from the prime mover. The above approach was employed to acoustically characterize two families of external gear pumps: the "Standard" family with spur gears, and the "Low Noise" one with helical gears, to determine the different noise emissions between spur and helical gears. Subsequently, the methodology was also applied to test a prototype of the Low Noise family: an external gear pump that implements design optimizations aimed to further reduce the emitted noise. The tests were carried out in 36 different working conditions, varying the rotational speed (from 500 to 2200 rev/min) and the working pressure (from 10 to 240 bars), for each pump. The results show that significant differences can be detected among all the tested pumps, with better noise performances for the two versions of the "Low Noise" family with respect to the "Standard" one. Moreover, the pump with an optimized design exhibits further improvements, reducing in a significant way the noise emission levels.