570 backfiring,popping

Here is my problem,if i am cruising sometimes the engine is misfiring and popping.
Full throttle,no problem at all,the time you let the throttle go it gives you this popping sound from the muffler.
The same downhill,but not all the time.
My Dealer like to convince me all of the 570′ engines are doing this.
He told me try other fuel,same result.
No codes,nothing.
What is your experience?