Well I think I may have to bite the bullet and take her to the dealership. I've triple-checked the tires, no rocks or nails. Crawled under the truck with the wheels turned at various degrees and no visible rubbing. CV boots are in perfect shape, no visible damage and no grease. I am running RokBlokz mud flaps front and rear, but plenty of clearance with the stock tires. I just know it's going to end up being something simple and stupid that I missed... but I'll be sure to update this so you can all laugh at me when I find out!