Found out my left rear torque box is ripping out of the car. The right side has a small stress crack but the left side is F'd!!!!!
Looks like I'll be getting a repair kit this week and bolting it in this weekend. It needs to be welded but my dads welder and my skills are not up to par.

I'll try to get pictures hosted of it soon, the torque box is virtually cracked in two.
All you Mustang guys check your upper and lower torque boxes. I have had a suspicion that my rear end has been moving a little too much over the last year or so and this appears to be the culprit.