2008 yukon Denali xl with the factory roof rails that came with it. Picked up a Thule Force XT Cargo box. It’s the big one. When we drive down the road, it bounces up and down quite a bit to the point where it contacts the roof. This is with and without cargo in the box. Seems like it’s the roof rails flexing. Is this normal? Does anyone else have this issue and is there a fix for it?