Front Brake squeaks and grinds on light breaking

I have a 2005 F-150 crew cab with a 5.4 L V8. It has 23,000 miles.

When I stop with light brake pressure applied the right front break squeaks lightly and at times makes a little grinding sound.

I pulled off the wheel and looked at the rotor, which has no deep groves or marks on either side. I looked at the thickness of the break pads and both inner and outer are thick with very little wear.

What could be causing the squeaking and grinding sound when applying light break pressure?

This does not occur with hard braking.