If I understand what you are saying, the muffler doesn't tighten up on the header? If this is right a couple things will help. 1) make sure the muffler isn't pushed on the header too far. The diameter of the header gets smaller. Make a mark 1 inch from the end and put the header on that far. 2) If using the large aluminum clamp get rid of it. They don't stay tight. RLV now uses a stainless clam p that does a nice job.