An aircraft includes a fuselage, a main entry door with an associated passenger loading zone, an auxiliary power unit (APU) in the fuselage, and an APU inlet assembly. The APU inlet assembly has an inlet duct, and inlet door, and means for redirecting sound waves coupled to or integrated with an interior side of the inlet door. The inlet duct has a first end coupled to the APU, and a second end associated with the inlet door. The inlet door moves between a closed position and an open position. The means for redirecting sound waves is positioned at a particular location on the interior side of the inlet door, and includes certain acoustic features and characteristics. The particular location and the acoustic features and characteristics cooperate to redirect sound waves generated by the APU away from the passenger loading zone when the inlet door is in the open position.