Looking online and talking to those who know, the current guess is the popping under 4,000rpm is from the stepper motor for the inlet. Doing some searches on the bike and in the parts manual I'll be danged if I can find it. Do I have one and if so where the heck is it? I have even had the airbox lifted up while replacing the oil pressure switch and no clue where it is. Or just tell me what hose to plug. If I don't have one I'll live with the popping as it does it less than my Mini.