Why does my brake pulsate?
It could any number of things. Here is a list of problems it could be. Your wheel bearings need to be adjusted or replaced, your brake calipers aren't functioning properly, yours drums or rotors may be warped. That is just a small number of things that would cause the brakes to pulsate.
Or it could just be the standard ABS brakes...
ABS Brakes. (they take some time getting used to.)