17-10-12, 01:56 PM
It's possible that the pad retaining springs are a bit loose allowing the pads to get jiggled back a bit while you're riding, when you apply the brakes they then clunk forward to their normal position at the front of the caliper slot. There is a mod some folks have done to the springs to improve them, but I've not seen pictures.
If it's not that, worn steering head bearings can give a similar effect under braking.
If it's not that, worn steering head bearings can give a similar effect under braking.