Chris, agree. In a tradititional helo, most of the noise comes from the interaction between the air from the main rotor onto the tail rotor blades. This is not the case in a shrouded fan, where there will of course be some noise from the MRB, and I seem to remember the fenestron being quite noisy as well. This combined with the engine noise makes quite a racket. For it to be 'eerily quiet' would appear to intimate that the engines were off and the noise of the fenestron assembly and rotor were absent.
Many factors will affect this though, for example, if the wind was relatively strong, this may alter the individuals perception of the noise. Too many variables, but food for thought.