<p>This paper investigates the effect of blade rake angle on the tonal noise produced by contra-rotating rotor systems suitable for use on small multi-rotor unmanned aerial systems (UAS). This investigation utilises semi-analytical, numerical, and experimental methods to investigate the physics of the noise generation mechanisms, generated noise levels and the psychoacoustic characteristics of this noise. Computational fluid dynamics (CFD) simulations and semi-analytical models are employed to predict the periodic unsteady loading on the rotor blades, and the loading data are used to predict the radiated noise for rotor systems with different blade rake angles. Experimental measurements of the noise produced by a rotor system with no blade rake angle were used as a baseline case, and predictions were used to synthesise and auralise the sound produced by rotor systems with different rake angles for psychoacoustic analysis. The results show that increasing the blade rake angle generally reduces the amplitude of prominent interaction tones due to the reduction in the unsteady loading along the blade span caused by bound potential field interactions as the blade rake angle increases. This causes a reduction in the perceived tonal noise level.</p>