Bhud, long shot...are you sure the visor is locked down? My GT Air can sometimes require a little 'persuasion' to lock into place, and it vibrates at speed if I've not got it all the way closed.
Mine too
I must admit I think the GT Air is one of the worst helmets I have ever owned for noise and turbulence its not a patch on the ancient Arai I retired - If only Arai did the internal sun visor :-(