When I hear strange new noises as my planes fly by I land and check everything out. So far it has always been something like a loose wheel, cowl, canopy hatch. Just little stuff. If you think you are having a control flutter then find the speed and do a close and slow fly by whit friends watching the controls, you can usually see the controls fluttering or the plane is reacting strange. Flutter is USUALLY found at the higher speeds. I have seen it so bad the controls were flapping at all speeds. If you have flutter it will strip out the gears in your servo pretty fast, not a good thing.