Guy's, I'm remodeling my bathroom, and when I did the mud on the sheetrock on the ceiling the first time, I had a crack along the seam about 3 ft long. I figured the next step of mudding would cover it, but it also cracked after drying. I've mudded and sanded 3 times, and everytime it dries, it cracks. I even tried sanding the crack almost back to the tape, and remud, but it still comes back. Any suggestions?