Vertical-axis wind turbines are an attractive option for small-scale wind-power installations. In this application, noise is crucially important. To investigate the problem, measurements taken from a model-scale turbine in a wind tunnel are considered. The sound radiated by the model is clearly evident in the cross-spectra from a pair of flush-mounted microphones. Parameter studies show that, in the normal operating range, speed is the dominant factor. The main source appears to be blade self-noise, although there are also indications of blade-wake interaction in the downstream half of the rotation path. Boundary-layer trips have a significant impact, showing that laminar instability is an important contributor to the self-noise. It will remain a risk at full scale, and its absence should be ensured at the design stage. To minimize the remaining sound radiation (at a given wind speed), configurations with lower tip-speed ratio at maximum power output should be preferred to ones having higher values of this parameter.