Flywheel woes

I recently swapped in a fresh rebuilt engine. Everything was great. A while later, I began to hear a tapping noise at idle, but would go away when put under a load. I pulled the tranny back, and the bolt holes where the torque bolts to the flywheel have been wallered out. Anyone know why this would have happened? What can I do to make sure it doesnt happen again. They were torqued to spec when it was put back in.

Loctite is your friend.