sounds to me like you are getting pad knock off. Its where the disk has been machined wrong and it wobbles. when sitting still the pads adjust and feel fine but when you drive the disks wobble and push the pads back to far. next time you press the brake the pads need two pushes to get them back to where they need to be. You may need to adjust the rear brakes aswell. To check the run out on the disks you should use a dial indicator. Hope this helps. Olboy