You are correct - greasing where they enter the receiver head helps quite a bit. But you also have to deal with greasy bars and receiver when you remove them. Ask me how I know!!
my inlaws came down with the bars greased. what a mess when i helped them unhook. its not like the noise is that bad. i really only ever heard it when maneuvering around the campground. out on the open road i never really noticed.
