sounds like your sub-frame bushings are going
there are 4 of them,,,,,, put the car on a lift then see if you can lift the rear end ,,,with a jack of course. it should lift the car not the rear end. if it goes up and down they are bad,,,before you try to jack the rear see if your finger will fit between the bushing and the body,,,after jacking again try with your finger ,you should have the same space call me and i can explain better than my two finger typing.