Disclosed is a flutter damper, including a chamber having an internal space, a movable diaphragm disposed at least partially within the chamber, the diaphragm separating the chamber into a first chamber and a second chamber, the second chamber forming an acoustic volume, wherein a size of the acoustic volume configures the chamber for peak acoustical energy absorption at a frequency range that is associated with one or more fan flutter modes, and a biasing member that moves the diaphragm responsive to a signal from an aircraft or engine electronic control (EEC) unit, wherein movement of the diaphragm increases or reduces the size of the acoustic volume of the second chamber.