I have the XD4 and when I wear goggles, with the visor shut, there is the slightest whistle at over 80 kph. without the goggles no whistle at all regardless of what direction my head is pointed , standing or sitting.
It is considerably noisier sitting than standing due to the screen on the bike (F800GS) but at 6'4" it probably was not designed for my height.
My old RJ's Dakar used to whistle very bad if there was a wind from approximately 45 degrees and it used to twist my head as well. No such problems with the Arai, I consider it money well spent.
Take it back, if they will not do something about it, hit them with it. That always seems to get a response.