All I found was the dreaded red x

 

I am guessing a rock stuck between the brake caliper and the rotor? (I can't see the pic either)

 

Thats my guess too. I believe I have the same issue, but cannot see anything externally or crawling under the truck. If it was a big hassle with disassembling brake components I'll just take it to the dealer.

 

So are we going to find out what it was???

 

Not sure about OP, but mine ended up being a rock in the brake assembly. It was larger than a marble

 

We have a lot of gravel roads and pick up rocks all the time. You can usually get rid of one by backing up and hitting the brakes.

 

I am having similar problem with an 999 expy 5.4. the squealing starts at 2000 RPM and usually stops at about 3000. This is new to me any suggestions or thoughts. I have been under the truck and noting lookes bad the wheels have a little give to them right and left but nothing to bad. any ideas would be appreciated