I'm having this issue on occasion not the popping and crackling you get from the exhaust when it's a bit lean I do believe it's a backfire into the throttle body and it's still due to being lean but lean down low not up high. As it happens at low revs sub 2k to me not at 3k+ so a very lean idle mixture to meet emissions regs. My 450 has a backfire screen on the oiled air filter to prevent this from igniting my filter.
Best fix would be a proper remap.
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