An unmanned aerial vehicle (100, 200) comprising: a first propeller operable to rotate and cause propulsion of the unmanned aerial vehicle, the first propeller generating noise while rotating; a first sensor disposed proximate to the first propeller and configured to detect the noise generated by the first propeller; a second propeller operable to rotate and cause propulsion of the unmanned aerial vehicle (100, 200), the second propeller generating noise while rotating; wherein in use, the first propeller and the second propeller are configured to rotate at independently varying rotational speeds and in a first rotational direction and a second rotational direction opposite to the first rotational direction respectively; and a control system configured to: receive a signal from the first sensor representing the detected noise generated by the first propeller and a signal representing a rotational speed of the second propeller; determine, based on prior modelling and the rotational speed of the second propeller, characteristics of sound waves produced by the second propeller; compare the determined characteristics of the sound waves produced by the second propeller to the respective characteristics of the detected noise generated by the first propeller; and based on the comparison, modulate the rotational speed of the second propeller, such that the second propeller produces sound that destructively interferes with the noise generated by the first propeller and substantially cancels the noise generated by the first propeller. a first propeller operable to rotate and cause propulsion of the unmanned aerial vehicle, the first propeller generating noise while rotating; a first sensor disposed proximate to the first propeller and configured to detect the noise generated by the first propeller; a second propeller operable to rotate and cause propulsion of the unmanned aerial vehicle (100, 200), the second propeller generating noise while rotating; wherein in use, the first propeller and the second propeller are configured to rotate at independently varying rotational speeds and in a first rotational direction and a second rotational direction opposite to the first rotational direction respectively; and a control system configured to: receive a signal from the first sensor representing the detected noise generated by the first propeller and a signal representing a rotational speed of the second propeller; determine, based on prior modelling and the rotational speed of the second propeller, characteristics of sound waves produced by the second propeller; compare the determined characteristics of the sound waves produced by the second propeller to the respective characteristics of the detected noise generated by the first propeller; and based on the comparison, modulate the rotational speed of the second propeller, such that the second propeller produces sound that destructively interferes with the noise generated by the first propeller and substantially cancels the noise generated by the first propeller. receive a signal from the first sensor representing the detected noise generated by the first propeller and a signal representing a rotational speed of the second propeller; determine, based on prior modelling and the rotational speed of the second propeller, characteristics of sound waves produced by the second propeller; compare the determined characteristics of the sound waves produced by the second propeller to the respective characteristics of the detected noise generated by the first propeller; and based on the comparison, modulate the rotational speed of the second propeller, such that the second propeller produces sound that destructively interferes with the noise generated by the first propeller and substantially cancels the noise generated by the first propeller.