When I was jetting my carb, I installed an oxygen sensor in the header pipe and it was attached to a fuel/air mixture gauge. This allowed me to see exactly what happens when I changed jetting. What was really a surprise to me is that the mixture ratio is not constant - but it changes constantly as the throttle is moved. At a steady cruise and steady throttle setting the mixture stays the same - but anytime you open or close the throttle the mixture goes slightly leaner.
When you open the throttle the amount of vacuum in the venturi drops and therefore a bit less fuel is pulled out of the float bowl......but this is just a temporary sag and the proper mixture recovers quickly. This is why we have a CV carb on the Savage - it helps to keep the vacuum from dropping too much when you open the throttle too quickly. (Some carbs have an accelerator pump that squirts a bit of fuel into the venturi to add the missing fuel).
When you close the throttle the engine vacuum increases on the engine side of the throttle butterfly - but the amount of air flow on the other side drops dramatically and as the slide drops the jet needle is closing off the fuel flow in that circuit.....the only fuel you are getting is from the pilot jet (idle) fuel circuit. The mixture goes really lean when you are decelerating and the throttle is fully closed - the TEV (Throttle Enrichment Valve) on the Savage carb is supposed to open and add more fuel to reduce or prevent the mixture from going so lean - but it does not work as well as it should. I am not sure if the valve was designed to work with E10 fuel - perhaps it would work better with pure gasoline.
You should not be jetting your carb for what it does with a "closed" throttle - your carb should be jetted for how it works while the throttle is open and the engine is making power......if your engine runs well, then don't screw around with the carb or jetting.
SUGGESTED SOLUTION - It is relatively easy to reduce the noise out the muffler while you are decelerating.
This is a primitive bike and a primitive engine and carb, and good Savage riders adapt their riding style to work with the bike. You need to become the "computer" that adjusts the fuel mixture as you ride - this bike will not do it for you like a modern fuel injected bike will.
As you shift gears don't slam the throttle fully closed. Gently roll the throttle off and leave the throttle open slightly so that you avoid the lean mixture and backfiring that occurs when the throttle is fully closed.
When you are decelerating and the popping/banging begins - open the throttle a crack just until the noise stops. You don't need to open it up so far that you begin to accelerate and need more brake - just enough for the noise to be reduced or eliminated.
With a little practice this will become second nature when you are riding your Savage. I have a Mikuni Round Slide on my bike, and it doesn't have a TEV or a CV slide - the slide opens/closes when I turn my wrist. If I ride this bike and allow the throttle to close fully when shifting or decelerating it really is noisy - it pops and bangs and backfires just like a poorly tuned Harley with open pipes.......but it I ride it and use my right wrist to control the lean condition while decelerating I can make it quiet.
There have been several riders on this forum who have had the same comment as you, and they have discovered they can easily control the noise when they adapt their riding style to better suit what Suzuki has given them. Maybe someday we will figure out how to make the TEV valve provide a bit more fuel when the high vacuum condition occurs - but for now we just have to adapt to the bike.
Try it!