The present paper is devoted to identify the acoustic characteristic of a multi-rotor MAV, and then explore effective noise reduction technologies for suppressing its high-level noise. It is found that the noise is mainly generated by the high-speed rotating propellers. Surrounding engine rotors with ducts designed to absorb their acoustic emissions is one of the methods typically used for reducing their noise. Thus two duct configurations, with non-perforated internal wall and with micro-perforated internal wall with back cavity, are designed, fabricated using 3D printing, and tested on a multi-rotor MAV. The acoustic performance of these ducts for achieving a quieter flying multi-rotor MAV are analyzed and discussed.