This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
firstname.lastname@example.org (Alvin N. Wang) wrote that he had a random clunk/think
noise while at highway speeds. He moved the load bars on his roofrack as
far to the rear as possible and it cured it. The noise had sounded like it
was coming from under the floorboards! A TSB may have been issued on this.