The backfire can be tuned out of you bike. What is happening is to much fuel is being delivered on engine decel. it is just a matter of changing a few numbers in the pcIII

 

ther are techniques to reduce or eliminate the backfiring but I wasn't going to go there, because there are so many schools of thought on tuning, it usually just invites an argument. Been using a PCIII for quite a while and I have yet to find a decel table, you need a little more robust tuner for that feature. Besides he said he was getting it dyno tuned and he didn't specify when the backfire occured. Personally I don't tune for sound, I tune for performance, and I subscribe to the theory that free flowing systems tend to have a little normal poping and backfiring, I'm not going to detune my bike to compensate for a litte decel crackling, just not important to me.