I think you found it.

 

Interesting thread. We ride with Bell Pit Boss (1/2) or Shoei J Cruise (3/4) depending on the day's variables. The Pit Boss allows far more wind noise due to our ears being uncovered by anything. The J Cruise really quiets things down tremendously for us. Exhaust notes are dramatically muffled and the wind (in ears) basically disappears. We've both commented about how quiet and insulated (from noise) our Shoei helmets ride. I will say our helmets fit very snugly around the forehead, temples and cheeks. There really isn't any opportunity for wind to push in there. We're riding with Pin-Lock shields and using the drop-down visor internally. Windshield is a 9" Long Ride Ultra Elite.

 

The best investment I ever made was a set of customer ear plugs. They cost about $60 at the local gun show, but they fit my ears perfectly and reduce any kind of noise. I've worn them riding, shooting, when the neighbor is being noisy, on the plane, you get the point. I can still hear people talking to me, but it takes the 'bite' out of loud noises. There are no special devices, just rubbery substance that fills my ears. Since they were made for my ears, they are comfortable all day.

 

 

 

I used to have a couple of helmets with the drop down windshield. I ditched them for a lighter model without the drop down. I also found the drop down screen was always soft plastic and scratched easily. The suggestions on different windshield, and maybe lower deflectors, might help.
My one modular helmet for snowmobiling is very noisy compared to a solid full face helmet.

I use those cheap yellow industrial earplugs for long hauls. I sprinkle some in my jacket & saddlebags. Of course I only have one ear that works, so they last twice as long and make me still "legal" in NYS. Because in NYS, it's illegal to wear earplugs in BOTH ears.

Try some of the cheaper suggestions and work up from there. And report back on your findings.

 

Have you tried tilting/rocking the helmet forward with the sun shield down , tilt until the S/S just touches the bridge of your nose, then tilt it back till it's just off the skin.

 

I have two 3/4 helmets, a Nolan and a Schuberth M-1. I don't have the problem you're describing with either one. The Schuberth has a sun shield but I don't use it as I wear prescription sunglasses. Looks like you're onto something regarding a cause for the noise however.

I should mention that I wear earplugs all the time when I ride, no matter if I'm wearing a 1/2, 3/4, or FF helmet.

 

I'll second your description of the J-Cruise helmet. Very quiet. However, I will sometime swear earplugs as my Cobra pipes can get a little loud on longer trips.

 

The Bells and Biltwells are quieter, they are smaller and are smooth on outside. I have a scorpion with vents and internal visor, very noisy. I have Bell 500 3/4 and even better is my Biltwell Gringo that I wear with no visor. Feels like open face, but with chin protection.