An unmanned aerial vehicle 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 , 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 , 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. <EOS>