Alot of the aftermarket exhausts don't do well at hiding the sound that the pair reed valve makes when injecting air into the exhaust loop to ignite unburnt gases when the throttle is closed when decelerating. So you could try running with the end baffle pipe, closing the reed valve intake or switch back to stock.
Just a small point of lexicography; "Backfire" is when the ignited fuel comes back up the intake system. When the ignited fuel pops when entering the exhaust to early and not fully ignited till it is in the exhaust, that is called "Afterfire". Most people switch the two, thinking afterfire is backfire because it comes out the back. Big difference, though, when speaking with a mechanic. Have a great day!
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