Mine seemed to be loose where they came out of the bottom of the pre cats.. the second time it happened is when I started getting more aggressive with the lock nuts and loctite... And added a hanger at the front of the system.Mine were very loose at the manifold. Not so at the muffler.
I was randomly searching the web and noticed is that quite a few people had that problem over the years and it seems that not having a hanger up around the front allows for more movement of the system.