Loaded up and headed to Ruidoso NM for spring break this year...
I use a Thule roof top carrier, before loading up the carrier I check the rails and make sure they are locked in place.
I check the cross rails for a tight fit, while running my hand along the bottom of the rail I found that the outer most screw was backing out, there are 4 per cross rail and 4 of the 8 were backing out..
It's a torx T-15...if you use your roof top carrier it might be worth checking them from time to time to make sure they are secure...

I suspect that mine worked loose from a occasional oscillation that I get on my Thule at highway speeds 65+ and a strong cross wind... the Thule will get to rocking back and forth...
Slowing down will usually resolve it... I do have a bug deflector installed, I haven't investigated if it has any impact on the oscillation.

Anyway... be sure to check your cross rails before loading them if you use them...
Sorry my picture is not better, I took it, fixed it and went on vacation before reviewing the picture...

 

That could ruin your whole day if the Thule became a "bad airplane".