Disk brake problem

[Stuttgartzerosix]

I am trying to get my front disk brakes to work correctly. Currently when the brake lever is pulled I hear a clamping metallic sound. I removed the brake pads, they look fine. Centered the caliper and adjusted as needed. All was fine the first 15 or 20 times then they went back the way they were. A clamping metallic sound with no braking what so ever. I am assuming I sound remove the main unit and caliper and clean? Any tips are welcome and thank you.

TG

[RobAR]

You removed the pads and inspected them - did not look glazed?
Are we talking Hydraulic or Mechanical?
All caliper mounting bolts are tight??