The pop at shut off is a trademark of the Savage. When you turn off the ignition the spinning engine pumps fuel/air into the hot exhaust header where it gets heated up and explodes in the exhaust.
I have not considered this before - but the header has an inner and outer pipe.....perhaps this allows the inner pipe to get much hotter than if it was a single wall pipe.
Allowing the engine to idle a little bit prior to shut down can sometimes help. A lean mixture tends to make a louder bang, a high idle speed pumps more fuel/air into the header than a proper 1,100-1,200 rpm idle speed.
My bike doesn't do it - some do. The noise can vary from a gentle "Woof".......to a loud shotgun blast!