the reason that you'r feeling the tapping in your pedal might be that when you hit a good bump or post hole while braking, the tire loses contact with the road for a split second. thats enough time for the computer to sense that the wheel is locking up since it doesnt have the force of the car pushing it down the road. the ABS feature kicks in and you feel the tapping in the pedal.
joe you're correct thats exactly whats happening - even worse if its wet out.. The computer is much to sensitive - there has got to be a way to disconnect the ABS i know the system is somewhat controlled by a computer but in even of some type of computer failure i know for sure you won't loose your brakes. i mean come on, you have a master cylinder and 4 callipers hydrolically opperated - i don't give a rats ass if disconnecting the abs turns on my check engine light - i will remove the bulb..