Not sure how your fender is, but my GM pickup started doing that. I fixed the outside, it bubbled back. When I finally pulled out the taillights to look, it was rusting from the inside (wheel side) out. The truck was past warranty, so I couldn't claim it, but keep in mind that "surface bubbles" might actually be coming from the other side.
Just put that in back pocket to ask if you get any flack at the dealer.
