To be more specific, I set the throttle curve to be 20% at mid stick. The pitch is about +5 degrees at mid stick. At this setting, I have a bit more power than I had with the stock motor. For now, it seems good for my level of flying experience.
I took off the blades, disconnected the tail motor, and spooled up the main motor in my hand to operating speed for about 5 minutes . . . no popping effect occurred. This makes me think the popping effect has to do with the tail. So, then, I reconnected the tail motor, and did the spool up again. Still no popping effect--the Alpha 400 runs great. After spooling down, I did notice that the mesh on my tail was pretty loose, so I inspected all the teeth on the tail gear. There are a couple that look a very little bit scuffed (I needed a magnifying glass to see this). It is hard to imagine that the tail could have skipped over a couple of teeth, but the evidence seems to suggest that maybe this happened.
At any rate, I tightened the tail mesh, and look forward to testing in the air tomorrow. Here's hoping . . . but if it still acts up, then maybe I'll have to consider the Tail Mix setting on the Rx.
Thanks for all your help, guys.