I bet it´s the front brake pads. The front tire (and rotors) are turning slightly when you´re pushing down on the forks causing the pads to rise off the bottom of the seat in the caliper. Then when you let off, it either turns back or the pads slip back down the rotor and click when they set back down in the calipers. My pads do that when I´m moving the bike around or washing it.