For me it's mostly engine noise, I ride off road 99% of the time and don't go that fast (20 or less mostly). I've tried riding with the Bose headset on just for a little bit as a test and it was perfect. if only someone would make a helmet that had those built into it. I have a nice Shoei Dual Sport helmet, but it's not quiet enough (for me).
Maybe an electric motorcycle is the only true way to get rid of the noise, but $12,000 seems like a lot to spend when really all I want is a quiet helmet... :)