Originally Posted by TOGA Descent
I have been flying various Airbus Aircraft for almost 10 years. I can tell you - categorically - the noise that you describe is the result of Speed Brake activation and typically occurs when the speed is above 250 KIAS, regardless of Altitude. It usually doesn't make this sound at low speeds, but is affected to some degree by outside air temperature.
Not having flown any Airbus FBW types before, it scares me to think that someone would be taking his speedbrakes at such low altitude that it can be heard from the ground. Whatever this sound is, surely it is cant be audible from 2500' agl?