My crossbars were very snug even without being tightened down. The crossbars have a very specific position. One each for the front and back. And, they have designated left and right attachment points. Either you may have reversed them front to back or turned it around… Or maybe the roof rails are not snug?
The installation of the cross bars was super fun for me. I ended up using a lighted mirror so I could see what I was doing. Just installed my Thule ski rack today as skiing starts here at the end of next week.