Spool valves are widely used in many applications, including the automotive field. The spread of more electrified vehicles requires silent components, including valves used in all the hydraulic on-board circuits. Valves are often affected by an unwanted phenomenon called cavitation. In this paper, an investigation on cavitation noise in spool valves has been conducted. For a defined valve geometry and different openings, the noise emitted by the valve varies with the flow increase through the valve. Therefore, bubbles onset and development can be identified by looking at the overall sound levels and the noise spectrums. In this paper a proportional spool valve has been studied experimentally, by acquiring the emitted sound due to the cavitation with a microphone. From the sound pressure level acquired for different pressure levels and at different valve openings, it is possible to clearly distinguish cavitating conditions from non cavitating ones.