Have a driveshaft shop check the shaft on a lathe, the same thing happened to me last year, I broke the 8 3/4 off the line the car shook bad, after that I was cracking the tail shafts every other time I took the car out, car did not seam to vibrate down track, I finally took the shaft to a shop and he said it was bowed in too places, you couldn't see it turning it in the car with a straight edge, after changing the shaft I never broke another tail housing.
Russ