I have an FM3a and whilst I love it, it isn't exactly the quietest mechanical camera I have ever owned. Try and get to use a Nikon FE, FE2, FM, FM2 or FM2n for less noisy Nikon MF cameras.
However, if you desire a quiet camera, a Leica M is the way to go. If you can't afford an M7, get an M6 and start getting some lenses. You could always upgrade the body to an M7 later.