sounds like the leaf springs are dry. I had the same issue on the 2007 CC classic. I had to jack the truck up by the frame, spread the leaves apart with a pry bar and squirted some axle grease between them. The springs got really quiet after that. There used to be companies that made leather "corsettes" for spring packs. You'd grease the spring packs up really good and then but a rawhide leather wrap around them and lace them up tight. It kept the grease in and killed any noise. Never had a rust issue and looked cool as hell. I know, I'm dating myself but you can't argue with what works.