Rear Driveshaft Coupler - Grenaded? Most Likely

so let me lay the ground here.
vehicle is in shop for "squeking" left rear middle of last month.
Guys at DCX dealership couldn't find what was wrong so they are going to replace all of the rear bushings this coming Monday instead.
So I get the car back from them that night and put about 25 miles on it. As I'm driving home with my older daughter in the car, I get on it and as the car shifts from 1st to 2nd, it sounds like the rear end took a rpg hit from underneath. I hesitated for a second to see if I lost power and driveability. No problems. Called the dealership the next morning and let my service advisor know. He says no problem Chris, just bring it in when we replace the bushings if you are not leaking any fluids or can see anything. So 3 weeks go by and then this evening, I am driving same daughter again, and the rear end sounds like another rpg hits the car on the underside. Pull over and check again. Can't see anything. Feels ok. So I call dealership as it is happening and left message that I am having problem with rear end of vehicle. It is shimming bad and the back end has a serious vibration.

new info:
Got a call back this morning that they'll be expecting me in. Told him of syptoms again and the vibration and that I think it is the coupler attached to the driveshaft and that the driveshaft has rub marks on it. "Go ahead and bring it in". Not go and have it towed in, go ahead and bring it it as in drive it in.
Sincerely,
cbutler32