Well we can close this thread finally. Took apart the entire crossover bean can system . The crossover pipe uses 2 sliding end tubes and 4 bolts with nuts to crush them onto the center crossover exhaust tube. Cut slits at the tightening areas were at their maximum for crushing limitations. That's why the bike started up quietly , then quickly became rattly as heat expanded that assembly. I took a Dremel tool with grinding wheel tip and cut the slots slightly more open. They now pinch down more firmly on the crossover tube and the header flange. Used Copper heat silicone on all fixing points. No more rattle !