Have you tried bouncing the rear of the car up and down to listen for the squeak? You might get a friend to help you. Have someone push down on the rear of the car, or jump up and down inside
, and the other person listen underneath/around for the squeak. Just don't get your head stuck under there
. It's probably one of the coil springs/perches or the bushings in the lower or upper control arms maybe. That's about all it could be. I don't see how the shocks could squeak. Just some ideas.