Noise in my 340

That's not an internal noise. Check the gasket below the #1 exh port. I'll bet it blew out. You want to check the header flage (the sealing flage) for flat ness, and whenever you torque them you staret with the center two bolts, then the inner bolts on the outer tubes, then the outer bolts. Tighten them. Fire it for a minute or so, snug them in that order again, the tihghten them the next day after it's been run. I use Mr. Gasket metallic silver gaskets. no prblems when the flange is flat and the torquing is don eproperly.