I very rarely sit in the back
, so I may not be the best person to give views about that. I think though that the beneficial effects of the MODERN fenestron are felt/heard mainly by those outside rather than in the helicopter.
In the cruise, the external noise from an EC135 is pretty good for a hele. It does get noisier in the OGE hover/slow orbit/ or descent though. On a noise basis I imagine that overall the MD 900/902 has the EC135 beaten..........