The fenestron already improved helicopter noise problems a lot (less tail rotor and main rotor interference) but this new blade tip they’re working with at Eurocopter seems like a great advance!
[youtube=http://www.youtube.com/watch?v=dBS1NRsYuF8&feature=player_embedded]
If the power levels / flight situations are the same in the two examples but the difference in the annoyance level of the sound is striking.
Now something similar for airplane propellers!