I have an 08 Super Duty that is making the most annoying noise when I am driving down the highway. The noise sounds like it is coming from the left side of the front windshield. It almost sounds like a faint horn going off. It is not a whistling noise but more like something humming from the wind vibration.

 

My F250 is also doing it. I think it is the drivers side door connector for windows and door locks. The connector has no gasket around it.

 

I had a noise like that - it took way too long to find - it was a loose piece of windshield moulding at the seem on the top drivers side on my 87 xlt Lariat.