A few years back, on a different forum (I can't remember which), a fellow showed how he filled the rib cavities with Hot Stuff spray insulating foam. When this had hardened he cut off the excess with a hack saw blade, flush with the rib profile, and cleaned up any other blobs that might have leaked out between the rib frame and the hood skin. Then he had Rino Liner sprayed onto the entire underside of the hood, including over the hardened foam. He indicated in his post that it quietened the 6.2 noise substantially. I have often contemplated doing this to my M1028.
Hope this helps.