backfiring

Hi everyone. I recently bought a 2017 RC 390 with only 700km on the odo. I was told it was totally stock besides some fork sliders and a tail tidy. However, I've started to notice the exhaust pops on deceleration. I've only owned one bike before so I'm not very mechanically savvy but I did a bit...

Need some help. I installed my Arrow GP exhaust and PCV, and I'm running the stock air filter. The PCV has the Arrow fuel map installed. When I decelerate, I'm getting backfiring. Is this normal? Is the bike running too lean? Too rich? Any help/suggestions would be appreciated. Gary