Ok, problem solved. I had checked everything I could, including the brake caliper bolts. I took the truck in to my mechanic and they used a listening device and found the sound coming from the caliper. They checked the bolts by hand and they were tight and no movement from the caliper was noticed. On a whim they decided to try the air gun on the bolts. The marked the bolts and then were able to turn them one turn with the air gun and verify they turn due to the marks. Problem solved. I was frustrated that I didn't find it myself but felt a little better that it took them a while to find it also, and upon initial inspection they thought everything was tight too.
