After hours of investigation, I have found the source of my whistling noise in the front of my 95 sport. When the vehicle was new my dealer installed a Ford labeled bug shield/wind deflector. This deflector has 4 small slits on the underside close to the screws that hold it in place. These slits are approximately 4.5" long and 1/4" wide. The air rushes up through the openings making the irritating noise. I taped them over with duct tape and have plans to permanently close them with silicon sealer. If you wanted to make your deflector whistle, the slits are the perfect solution. Maybe they doubled as deer alert whistles.