Morning....................okay, driving the truck at various speeds, a loud metallic screeching sound comes from the front left side of the truck. When I slow down to almost a full stop, the sound goes away suddenly. I can feel a "thunk" through the brake pedal. I go on my way and the sound is gone. The sound comes back if I drive any distance. Totally variable. But it happens every time I drive more than 10 miles, sometimes when I drive less. A mechanic took a look and cleaned the rust of the rotor and replaced the clips on the caliper ( I believe that's what he said) But he was up front, charged me nothing and said he's not sure what causes the noise ( he heard it on a test drive) So, everyone, what is this noise and what does it mean????? Many thanks.