The noise or chirp is coming from the brake pad free floating on the anti-rattle clip. With light pressure applied, the play or float is eliminated so no noise. You'll also notice if you hit a few bumps, when you press the brake, you'll get a quick chirp, moving the pad.
I can't tell you how to fix it though
. Mine has been in a few times for this. Some grease on the pad lobes at the clip helped for a few miles, then they replaced my pads and installed a new style anti-rattle clip that helped for a few miles and now they've replaced my calipers but that did not work. Not sure where they can go with it at this point until they figure out a new design.