Oscillating-water-column (OWC) is the most developed technology for wave energy conversion, and several prototypes have been deployed and tested on the sea. An important aspect of the long term environmental impact assessment of this technology concerns noise emission. The power take-off system of an OWC comprises a self-rectifying air turbine connected to an electrical generator through a shaft. The paper presents a comparison between the noise emission of three types of self-rectifying air turbines: biradial, Wells and axial impulse. The data for the Wells and axial impulse turbines were collected from the literature. The noise emission of the biradial turbine was measured at the Instituto Superior T´ecnico variable-flow test rig. Acoustic measurements procedure were carried out following ISO-3746 guidelines. Results show that the biradial turbine specific noise level is lower than of the axial-impulse turbine and Wells turbines.