I've been flying A319s a lot lately, and they all seem to make a loud buzzing/groaning noise when the engines are throttled. It starts on takeoff and persists through the flight. I previously thought that it was related to some piece of plastic in the cabin that was loose and vibrating on one particular ship, but every A319 I've flown in seems to make this noise, making me think it is something else, and the Mrs. seemed annoyed by the sound last time. I seems like it comes from somewhere in the cabin instead of the engines. Does mtrainer90 or anyone else have some insight as to what that annoying buzzing sound is?