Had exact same cracking on right hand pipe and support of decat. Pipe man suggested to get rid of front clamps to allow little movement. Similarly the two decat pipes are separate pieces, not welded or clamped and can slide a little.
Quietly adding to my collection of "challenges" here - while doing a post ride clean this morning have found the bracket on my early version decat pipe almost broken through. Time to look into a rubber mount.
There should already be a rubber mount in the frame . I think this problem has been solved with the NOT tight bolt / double nut method ? When finished the bolt should spin when turned with your fingers , but not so loose that it slides back and forth . We've posted this some time ago. Others talked about leaving the clamps loose at the entry to the x-pipe , I do not do this.
Thanks Tony, i had looked a bit closer and read a bit more after posting above, good to have it confirmed. There is so much info on here i am not always sure that i have read the latest info.
Spin but not rattle, same as setting the tappets on my ES2