like Trey said , check caliper bolts, but don't overlook the brake pads anti rattle springs.
If these babies were omitted at the last brake service, the pads move freely in the brackets, thus clack,clack.
On the same lines of thought, if you have aftermarket pads installed, sometimes they are physically smaller ie plate size=loose.This gives the same result.

Once the pad shifts forward, it stays until you roll backwards...this is why you hear it under 1st stop..
Just an idea.