I experienced this on the 5S too but at times I feel like the home button is loose and has a crunchy feeling to it. It doesn't happen all the time but about 20 % of the time and if I press it consecutively 4-5 times it goes away. Sometimes i can just lightly touch the button and feel some sort of a layer move before the button starts moving in. And alternatively sometimes when I release the button after a press I'll feel a last motion when my finger leaves contact. Is it just me? I recall experiencing this on the 5S and the 6 too.