In this work, we investigate airfoil tonal noise generation and reduction by the means of streak generators in form of cylindrical roughness elements. Roughness elements attenuate tones in the acoustic field for the case with chord base Reynolds number Re=80,000. Further, the coupling between structures generated by surface roughness and instability modes (Kelvin-Helmholtz) of shear layer has been identified through stability analysis, suggesting stabilisation mechanisms of Kelvin-Helmholtz instabilities by which the sound generation by the airfoil is reduced by the roughness elements.