Typically the bumper/hood gap is cause of whistling in 9x6s (in 9x7s it's side mirrors). Quick test... put a piece of painters tape over gap from bumper to hood and re-test.
If no whistle sound then your issue is there. Proceed to remove tape and using the two upper most screws for bumper (under trim where hood latch is), adjust gap from bumper to hood. Visually you *think* it should be same as gap b/w hood & fenders but from factory it's actually about 50% larger than those on side. That said, you can also adjust hood's closing height too to ensure it's below the bumper. Pull back frunk carpet and adjust by loosening the two 10mm (IIRC?) nuts holding the latch receptacle a bit lower. Small increments here are all that is needed here and don't forget to also adjust the black rubber screw-in bumpers in corners of hood.
Good luck
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