Sound deadening in 1975?

Did something happen in 1975 to the sound deadening of the a-bodies? My '75 Duster trunk lid shuts and opens very easily with a quiet click, just like a modern car, doesn't have the normal hollow clunk I'm used to with my old mopars. It's not down to adjustment. Looking at it I can't see any difference with my previous dusters or darts, was the lid filled up with sound deadener? I noticed there's a bit more splashed around inside the trunk than my older mopars.