I second the earplug concept. There are 2 options that I know of for helicopters, the Clarity Aloft and the QT Halo (
http://www.anr-headsets.com/Html_folder/QT-HLO.html). I have that one, and like it. Much more comfortable and better than my DC ANR headset. They are also very reasonable priced relative to other ANRs and the Bose system.