Knocking noise after new exhaust gaskets

Ironically enough, I had this happen one time. Customer brings in 68 Charger with a freshly rebuilt 426 Hemi. The left exhaust manifold gasket was wasted. Was extremely loud. Fixed that and then heard a lot of valve lash from the right side of engine. Number 6 intake lifter was wasted too. New engine time. Hopefully this is Not your problem.....