I believe the rear brakes are bad

Here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-replace-rear-brake-pads-and-rotors

Below is the process from the manual that will give the detail that you need to run through this.

Please let us know if you have other questions. Thanks

Hello, I'm Danny.

Usually what we ask people to do when it comes to noises or rattles etc. we ask for you to make a video of the sound and upload it here. Here is a tutorial for you to view on how to change rear brake pads and rotors:

https://www.2carpros.com/articles/how-to-replace-rear-brake-pads-and-rotors

I've attached picture steps below on how to change the rear brake pads on your vehicle. Hope this helps and thanks for using 2CarPros

Hi,

Replacing the brakes and rotors isn't too hard. First, here is a link that shows in general how it is done. You can use this as a guide.

https://www.2carpros.com/articles/how-to-replace-rear-brake-pads-and-rotors

Here are the directions specific to your vehicle. The attached pictures correlate with the directions.

_______________________________________

2006 Kia Optima V6-2.7L VIN 4
Rear
Vehicle Brakes and Traction Control Disc Brake System Brake Pad Service and Repair Procedures Rear
REAR
REAR DISC BRAKE

COMPONENTS

pic 1

REMOVAL
1. Raise the vehicle and make sure it is securely sup ported. Remove the rear wheel.
2. Release the parking brake.

pic 2

3. Remove the guide rod bolt (B). After raise the caliper assembly (A), support it with a wire.

pic 3

4. Remove the pad shim (A) and pad assembly (C) from caliper bracket (B).

INSTALLATION
1. Install the pad retainers to the caliper.

pic 4

2. Check the foreign material at the pad shim (A) and the back of the pads (C).
3. Contaminated brake discs or pads reduce stopping ability. Keep grease off the discs and pads.
4. Install the brake pads (C) and pad shim (A) on the caliper bracket (B).

pic 5

5. If you are reusing the pads, always reinstall the brake pads in their original positions to prevent a momentary loss of braking efficiency. Push in the piston using SST (09581-11000) so that the caliper will fit over the pads. Make sure that the piston boot is in position to prevent damaging it when pivoting the caliper down.

pic 6

6. Pivot caliper down into position. Being careful not to damage the pin boot, install the guide rod bolt (A) and tighten it to the specified torque.
7. Install the brake caliper.
8. After installation, check for leaks at hose and line joints and connections, and retighten if necessary.
9. Depress the brake pedal several times to make sure the brakes work, then test-drive.

NOTE: Engagement of the brake may require a greater pedal stroke immediately after the brake pads have been replaced as a set Several applications of the brake pedal will restore the normal pedal stroke.

_______________________________________________

I hope this helps. Let me know if you have other questions.

Take care and God Bless,

Joe

This video shows the job being done on a similar car but the process is the same.

https://youtu.be/7a-scFGaYT0

Here is a guide to help you step by step with instructions in the diagrams below to show you how on your car.

https://www.2carpros.com/articles/how-to-replace-rear-brake-pads-and-rotors

Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

Check the surfaces of the rotors. If they are smooth, you need not do anything with them. Check the edges for the amount of wear. If they run too deep, the rotor might be too thin and requires replacement. Measuring them would be the best idea.