get a repair manual, and what the hell is a "rattering noise"?

if you mean grinding, then you need more than just pads, my suggestion---

take it to 2 different places that give free or cheap brake inspections, make sure that you talk to the guy that inspects your vehicle, and get a copy of the inspection sheet they fill out

if both places tell you something different, take it to a 3rd place and so on

do not start working on your brakes until your first know whats wrong with them

and as always the brakes are THE most important system on your vehicle, do not take working on them lightly