On my 03 Sequoia. Ordinarily I'd suspect caliper guide pins but this is a 4 piston fixed caliper. Maybe inner pistons seized? Odd thing is, 99% of the time, it brakes normally with no noise. If I have to make a hard stop, afterwards it makes the metallic grinding sound as the outer pad metal is scraping the rotor. That goes away after a few miles and it's quiet again.