Hi Paul. I'm no specialist in this but the sound on pulling away could just be a fracture in the exhaust system as the engine rocks due to load. Cruising entails little load on engine so the fracture may not be evident then. If it is a fracture, it would be wise to check engine mounting bushes in case a replacement is needed.
As for the rear end knocking, search this site, there's lots about this, usually bushes in the drop links.
Hopefully someone more knowledgeable will reply.