1999 GMC C2500 noise ?

I recently purchased a 99 gmc p.u. At highway speed there is a sound like a flag flapping in a strong wind, on each side of the truck . It sounds like its coming from the area where the hood hinges are attached. Ive removed weather stripping and secured loose plastic pieces and even stuffed rags into holes in that area . I have not been able to find it, and any of my attempts have made no difference.
thanks
spike