Disclosed is a gas turbine engine including a fan, a nacelle including a flutter damper forward of the fan, the flutter damper including an acoustic liner having a perforated radial inner face sheet and a radial outer back sheet, the acoustic liner configured for peak acoustical energy absorption at a frequency range that is greater than a frequency range associated with fan flutter, a chamber secured to the radial outer back sheet, the chamber in fluid communication with the acoustic liner, and the chamber configured for peak acoustical energy absorption at a frequency range associated with fan flutter modes, and the engine includes (i) the nacelle and a core cowl forming a convergent-divergent fan exit nozzle; (ii) a variable area fan nozzle capable of being in an opened and closed, the opened position having a larger fan exit area than the closed position; and/or (iii) the fan being shrouded.