I had the same problem on my 1998 Megane. Usually the plastic gears in the flap system break, so the whole unit should be replaced which is expensive (600-700 EUR). You can simply disconnect electric supply to the unit (connector which is about 20 cm from the battery, just below the front screen). The 'banging' will eventually stop and then you will live without air recirculation option.
Vladimir, February 2009