Smittyff

I have a 2002 RX300 with 140,000mi, I am the second owner of this vehicle. Recently as I am backing out of my driveway there is a loud clunk and it only happens when the car is cold. I thought it was the spare tire or iron in the back moving around but I have secured those. I cannot for the life of me figure it out. My dad thinks it is the ball joints going bad but I am not sure. Any help is GREATLY appreciated! Thank you for your time Chris Smith