If the noise is coming from the rear wheel it certainly is not ball joints. Ball joints are located on the front wheels. You should look under the car for wear spots. Is your shock in good condition. Take the wheel off and check the brakes. Are the brakes dragging? Also check condition of brakes they may need to be replaced.
If it sounds like a squeeky bed spring it's possibly the ball joints. Our truck was squeeking in the front end like an old bed. That's what it ended up being.
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