I was thinking the same thing and/or doing the cutting holes thing to change the wind pressure behind the screen.
Also the the helmet peak seems to vibrate a bit too. I think this causes a low frew vib to be transmitted to the helmet (XD) then to the ears. I can put my finger on the peak and the low freq. noise seems to be reduced about 50%.
here are my specs
05 model with stepped gel seat
Arai XD helmet
Euphoria is state of mind