Are you running a hood? if not are the hinge retainers still screwed down? the open end of the retainer may whistle... . when hunting with dad he always made sure i had a spent rifle shell in my pocket, blowing across the open end 3 times was a hunter's SOS...
Being perfectly honest here, I have never owned a car that din't have some wind noise, ether from the visor on model A's or the windshield on my '32 sedan, heck even the '54 ranch Wagon has some from the vent window's, I have replaced the rubber and done everything I can think of and the noise still exist.. I have learned to live with it. HRP
I was given one and found a mate on ebay... they were 2" longer than stock swing arms... lets it swing way out/up and really cut down the wind resistance... holes in my visor would also help...
That's the beauty of grandkids. He'll repeat it at home and then you will catch hell for it. At least that is what happens around here.
I actually teach him things like that hoping he will repeat them at home. A little payback from time to time.