Fresh air leak somewhere in the exhaust system is first thing to look for if the deceleration popping is new.
What type mufflers are you running, OEM?
More open exhaust will have some deceleration popping that the OEM exhaust with the OEM CAT(Catalytic converter) will cover up.
The Loopz install removed the CAT from the system thus allowing more exhaust notes to be heard, one being deceleration popping.

Do you blip the throttle when down shifting?
Blipping throttle while down shifting may also cause deceleration popping. Blipping the throttle is not something you need to do on an EFI system(Electronic Fuel Injection)... When you blip you are telling the ECU(computer) you are speeding up and more fuel is injected, while really you are slowing down and don't need the excess fuel.
I know most of us are used to blipping to match gear speeds on the down shift and to clear a carbureted system, but throttle blipping is NOT needed for EFI systems and the gear box on the F6B down shifts just fine without blipping.
Being old school I had to break my now bad habit of blipping when I got my first EFI steel steed(VTX1800c) and later when building an aftermarket Fuel management system for the VTX1800 I encountered may issues related to blipping the throttle and when blipping was stopped many of the problems were resolved.