Just fired the N90, F100, Elan, Robot, and Leningrad. The drives on the N90 and F100 are essentially silent, with the F100 having a slightly quieter shutter. The Elan has a slightly quieter shutter than the F100, but while the motor drive is very quiet, it can be heard. The Robot whined a bit, but that may be a function of being over 60. The Leningrad doesn't whine, but has a quite noticeable thunk at the end of the advance. I think you would be hard pressed to find something much quieter in use than an F100, unless you go to a leaf shuttered rangefinder.