To add to the speculation,
The Tenni has recently developed a sneeze, though I called it a cough. Rare, but there. When hot and upon rev from idle.
Before: (ran perfect) stock cans FBF Xover, BMC filter, PC3, dyno tuned.
After (coughs) same as above but swapped in Stucci for FBF, and added MG Ti cans. not the Ti ECU, no changes done with tuning yet. Done about 150mi. since swap.
Still runs great. Just the sneeze. Obvious to me, a response to the cans. New tune in the very near future.