Sounds like maybe your rear brakes aren't adjusted properly. If this is the case, I believe the rear drums on the Kia are self-adjusting, but i'm not sure. If so it should improve over time. Or it's possible air in the lines. Squeaking could be from the new brakes themselves, did you go cheap on the pads & rotors? Many times cheap aftermarket brakes tend to be squeaky. A little lube on the back of the pads, where they contact the caliper, will sometimes help.

Keepin It Awesome