This was one of the reasons I chose a Scorpion helmet for my new el cheapo helmet. According to reviews on Sportbiketrackgear.com, most full face helmets are designed with a leaned forward, sport riding position in mind. So if you sit upright with the vents open you often get a whistling noise that goes away if you lean over more, and you don’t get much airflow. But with Scorpion EXO 400 and 700 models, that’s the opposite. You get the annoying noise and dereased airflow while leaned over because the vents are more positioned for upright/standard riding positions, which I thought was a good idea since I have an SV650.
That being said, I’ve owned 4 helmets so far and I’ve discovered that the leading cause (based on my personal experiences) for unwanted helmet noise is when the visor doesn’t seat properly while closed. The Shark RSi and HJC I had were especially bad with this. The Scorpion EXO 400 and Shark RSR2, not so much.
My next helmet will either be a Shoei RF-1100 or Icon Airframe.