Since the issue is at the pop, the easiest solution would be to add some length of crossfade at the split point. This should be compatible with an “indefinite sustain” loop region, for example:
In this case, I have the beginning of the sound, and a loop of the tail with a transition region that crossfades the loop. To account for the pop, I’ve split the beginning and tail, extended the ends of the split point to overlap, added a crossfade between the two. Depending on the sound, you may want to adjust the crossfade durations or starting position of the loop region, but you should be able to address the pop with this.