Front end flapping noise

Assuming this noise sounds like something that is loose, it is more than likely this is a fender liner that is loose that when you reach the proper speed it is just moving around in the wheel well area.

What I would do is try to pinpoint which side of the vehicle it sounds louder on and then remove that wheel and see if this liner has all the proper clips.

You will have to jack the car up so here is a guide that will help with this:

https://www.2carpros.com/articles/jack-up-and-lift-your-car-safely

You can even remove it if needed and then test drive the vehicle to see if the noise is gone.

If it is then you will need to reinstall it as shown with all the proper screws and clips.

Please see below for the detail. Thanks