How do you avoid that Horrible vibrating noise while driving down the highway! I have a Subaru with a rack on top with two cross bars. I bought two foam velcro pieces from Dakine to go over the cross bars. Then lay the board on top and tie down the front and back with the straps directly to the rack. Everything is real tight and the board is not moving at all. But as soon as I hit 40 MPH it sounds like there's a drill on top of the car. Is there a way to avoid that?