I'm no expert but the popping as has been noted here earlier, is definitely from starting your forward stroke too soon, and the leader piling up, can also come from too limp of a leader in the butt section, also extra long leaders can magnify this. Also be sure to use mono intended for fly leaders, it is stiffer than regular mono. There are many tapered leaders out there, what I'm saying is you could have ten leaders all the same length, and strength, but all have different stiffnesses. If you want a leader that helps you avoid the pile up problem, I would lean toward the stiff side, so as to turn your fly over easier. I have struggled with the pile up thing too, and this is how I deal with it.