97knightrider

I need some help, car started making a crazy like metal rubbing on metal noise when I reversed with sharp turning. Now is happening more often. I took a look under with car on ramps I didnt see anything out of place. I took it to sears they saw nothing and recommended pep boys, so I took it there. They said it was a piece of metal was rubbing on the drive shaft and they bent it out the way. The noise never got better, so I took it back and they couldnt figure it out. I put new rims on the car today and I saw one of the rear sway bars bushing is torn could that be it? How about the u joint? would that make that noise? I hope its not the rear end!>?