Any significant air leak will cause exhaust to detonate from drawing fresh air in during deceleration. If it came loose and you didn't get it sealed back up properly it may be leaking. Triumph uses wire mesh as a crush gasket around flanges, take it back apart and make sure it's not deformed or folded up. It may be necessary to either "fluff up" the mesh so you can crush it again, or use a sealant to stop any leaks.
I used an exhaust putty to seal up my TOR's to stop the popping during decel, works good formed into the wire mesh.