I was persistent with my dealership about the whistling from my car and got an experienced technician to drive around with me... this was after I had tried to get them to listen to some recordings. I was almost positive it had to do with the steering because it would get louder as the steering wheel was being turned.
The technician told me that it was the plastic intake. He said that there's probably defect/bump in the plastic that's causing the whistling. He also said that a lot of GM trucks had this issue at higher revs (mine was at a very low rev). He pointed out that when stopped, the whistling gone/faint, but as soon as the revs get a little higher, the whistling will start.
I hope this helps someone..