There is a good chance that you need to replace the pads on the rear. Try to find a set that is considered dust free. They are more expensive but worth it. Be sure to apply the membrane on the back of each pad before installation. This will cut way down on the squealing sound both going forward and in reverse. Hopefully your rotors are in good condition. Rotors are relatively cheap and if your current rotors have enough thickness left they can also be re-finished/turned. One final thought: spend the extra money to buy quality brake parts if you can.