This paper gives an overview of work investigating the noise produced by the propellers used on small multi-rotor unmanned aerial vehicles (UAVs) which has been recently undertaken at the University of Auckland. There are a number of different physical mechanisms by which these propellers generate noise and these have been studied using computational and analytical modelling and experimental measurements. Sources of noise which arc covered in this paper are: steady loading and thickness noise sources for isolated and shrouded propellers: unsteady blade motion: turbulent inflow for isolated and shrouded propellers: unsteady loading due to propeller-strut interaction: and the unsteady loading on the blades of a contrarotating propeller. The paper also describes some recent work undertaken to develop a standardised method for measuring noise from UAVs which includes assessing the suitability of ground-board mounted microphones for outdoor noise measurements and identifying appropriate metrics for quantifying UAV noise. The paper concludes with suggestions for future work.