Cracking of rear fender?

I was out this morning starting a swap of my POS chrome bumper for a new black bumper. I noticed some cracking on the rear passenger side fender in the area that is partially concealed behind the bumper wrap around at the corner of the vehicle.

has anybody seen anything like this? There has been no impact damage, and I have owned the truck since new (ordered it and picked it up with 2 miles on it).

The failure looks like fatigue fracture to me. Starting at a stress concentration between the corner and the edge. If it is fatigue, what loading does it see? Not much more than aerodynamic flutter going on in that area. It is all the way through the thickness of the panel.

There are 226,405 miles on this 2006 Doublecab TRD.

I was thinking about taking the truck to a body shop to have them touch up my 226k worth of rock dings on the truck, would this be very expensive to have fixed?

Photos

 

Just wanted to add that there is no rust on the break. Here is the southwest, it is so dry that few things rust fast.

 

is it still under warranty?

 

I noticed in your avatar that your truck has a cap , has that been on the whole time ?

I had an old Ford Ranger with a lumber rack on it and the box broke eventually along the same lines as this , I attributed it to the fact that as the weight came down going over bumps , it would force the bedside out as the only thing resisting this movement was the tailgate .

I wonder if the same issue could be caused by your cap .

 

Thanks. Yes the cap (Snugtop Supersport) has been on since day 1. I'm not sure how the load from the cap would be through the corner of the sheet metal on the fender though.

 

No.