The amazing bulging billet grille!

[apstguy]

Ok. This one just plain defies explanation. See if you come up with an answer because this stumped me.

I went to Ceres today. (15 min. down the freeway) When I got to where I was going (work) I walked by the front of my truck. I did a doubletake, gasped, and cussed. My billet grille was bulging out! The thing looked like someone had pushed on it from the backside making it bubble out! I cussed again. WTF??? This happened on the freeway? Air travels the other direction! I thought maybe my core support colapsed somehow, but I popped my hood and it was fine! I hadn't done any work on it in the past couple days putting pressure on it. I simply pushed on the front and shoved it back in. Looks perfectly fine now.

If someone can explain this I think you deserve a prize. Thoughts please!