While I was driving yesterday I heard what sounded like something breaking or cracking underneath my stang. As soon as I heard that a real annoying sound started from the drivers side rear which was like the sound of a rusty gate opening and closing. It seems to happen when pulling in/out my driveway or over when on a bumpy road. It even did it when my car was off and I got out and when I pushed down on the back end. Could it be a bad shock?