In recent years there has been a growing interest towards Unmanned Aerial Vehicles (UAVs). They play a central role in a wide array of industries, with examples in the medical sector, search and rescue operations and parcel delivery services. While they are attractive thanks to several of their characteristics, such as cost-efficiency and manoeuvrability, the noise they generate is still an obstacle to their widespread acceptance. Several propulsion configurations have been assessed to tackle this problem, and a substantial research effort is directed towards shrouded propeller systems. While the increase in safety due to the presence of the duct is clear, there are still open questions related to their aerodynamic performances and noise signature.