Agree with dalan here. Think about bending the bar towards the back around your legs. You don't actually do that, of course, but the cue helps tighten your lats, which keeps the bar against the legs while simultaneously keeping the back locked. When you do that as part of your setup, that's when the bar lifts and "clicks" inside the plates, taking out that slack right before you peel the plates off the floor. Steve Ross covers this well in his article "
Lats in the Deadlift."
BTW, great job on making the quick adjustments and getting that third set in!