As far as I can tell, the FE, FE2, FM, FM2 and FM2n have exactly the same sound quality as the FM3a. That is to say, it's not very loud but it's of a certain pitch that is noticeable; of course all this gets much much worse with the MD-12 attached. That said I enjoy mine a great deal. Whether it's useful for being quiet in weddings is hard to say. Play with one in the store? There are some older Nikons that have cloth shutters (the F3 comes to mind) that might be quieter, or at least of a different pitch.
As for quiet, the quietest camera I own, bar none, is my TLR, which has a very soft click noise when the shutter goes. Sometimes I miss it and I'm the one shooting. Leicas have nothing on good TLRs. You may not like the lens selection, though.