When I ever so lightly tap my AEA R84 Ribbon mic there a rattling metallic sound (similar to how a vacuum tube sounds when it's "going" and you tap on it).
The good thing is the factory is in Pasadena, CA (about 46 miles from me). I bought the mic 16 months ago and have been very loving and gentle with it (pop screen and cover it when not in use). If it is out of warranty work required and it is the ribbon, it seems it will be $140 to fix it.
Prolly take a drive out there tomorrow to drop it off.