helmets are always a trade off.
The only way to get a quiet one is to have no vents and very littleto disturb the airflow around the helmet.
If you look at the Roof (as an example) it will be fairly quiet compared to say my RX7. Why, next to no vents BUT this causes other problems that IMHO are far more dangerous. Lack of vents means misting problems and everyone I know that has Roof helmets have misting problems. Maybe not an issue if you only ride in arm weather but if like most you encounter variations then this is a big issue and certainly more of an issue than noise.
Second problem is that the lack of vents means the helmet is going to be very warm, no good if you ride in warm climes!
Basically you can have good ventillation and cooling with the clear visor that promotes or you can have a quieter helmet. Unfortunately no-one has managed to come up with the all in solution yet
I have a cheap shark that I got when I was waiting for my RX7 to be specially imported from Japan. It is quieter but again has less vents though I would guess still better than the Roof or its like.