Car vibration when brakes applied(stoped)

[tyrantfour]

ok so i have this problem with noise and vibrations. when i start my car in neutral there is a slight vibration not that noticeable and not always, it changes frequencey so you dont always hear it.

however when you put it in D with the brakes applied it lurches forward and the brakes and then gets loud and shaky, the shakieness sounds like its coming from somewhere in the dash but its nothing i can pinpoint from the drivers seat with the brakes in.

in R, the car is as quiet as a mouse, you can still hear the engine of course.

so i guess my question is, once the torque gets to my rotors and the calipers stop it there, where is it going next? whats the next vulnerable spot for vibrations?
thanks for any help!

1990 mustang lx 2.3L auto bone stock save for a 8.8" rear