If it's bubbling above the flares, you don't want to see what is behind them. Very common place for road salt to deposit and chew away at the fender till there's nothing left.

 

You'd think for as much as we spend on a vehicle now a days that they could make a bed that DOESN'T rust at the fender wells. I had two Dodge RAMS that did this and the body shop said I would have at least $7,000 tied up in metal work and paint. I traded them both. Makes me want to buy a Ford with an aluminum bed on it.