When you say crackling, where does it come from - back end or the front? I can make mine pop out the back, esp changing from 2nd to 3rd, if you boost up to around 3500-4000 and hold it without the bov venting so the pressure stays up which sounds like what you're experiencing. Slight blip on the throttle as I'm changing seems to do it. I suspect it's dumping a bit of unburnt fuel into system so maybe you can hear it more now with the bigger pipe than before???

I also had to get my dump pipe repaired some time ago as it had actually cracked, so all the noise was coming from the front like the exhaust system had been cut off lol

(I try to pop it deliberately sometimes haha, sounds cool but might not be so good for the system... although I have 3" with K04 which would make some difference too)