Had the same squeak. Couldn't see it but plenty annoying. Look for the extra rust streaks that should be there or will soon be. The top of the upper bumper and the [62242P] RETAINER-FRONT BUMPER UPPER CENTER were rubbing.
I fixed it by lowering the bumper bracket a little bit. Just loosen the frame rail bolts on each side, lower and re-torque. if that dosen't fully cure it, you may have to raise the retainer a hair. They are very close together up in there and with the plastic cover on, it's difficult to tell where one starts and one ends.
Click the thumbnail. I circled the metal retainer and dotted to the upper bumper where they rub when put together. I use blue threadlock for just about every bolt on the truck.