I don't know if it's the anti-rattle clip, but definitely get this replaced.
In my old truck, a '94 bravada, I had the same slight squeak that went away when I touched the brakes, and thought nothing of it for the longest time. By the time I had it checked out, it ended up being that I needed replacement of rotors, calipers, drums, and all hardware.
Basically, the subtle squeak turned into a $480 problem.