actually there was an asphalty fibre material glued to the roof metal from the factory - you don't want to shim between the roof panel and the headliner bows, you want to get some of the peel n seal folks have discussed here and stick it to the roof in sections between the bows, then if you can afford it someday, get a headliner made for the truck - what's happening is called 'drumming' and happens on all large 'un-ribbed' panels like the panel truck roofs, even the doors
Bill
