Okay, I think maybe I've figured this out... What I thought was a problem is actually a feature.
Since the A2A Accu-Sim sounds were playing through my headset instead of my speakers to begin with, some of them sounded a bit strange and too loud. Now that I've got them playing through the speakers where they belong (THANK YOU Cody Valkyrie!!), I believe the 'chatter' I was hearing is simply valve clatter, and is intended to enhance the sound of the engine. It's the fact that the sound was cutting out
that was the problem.
I still lose that clatter sound sometimes, but now it's usually not till I've been flying for at least an hour or two -- not within just a few minutes, as was happening early on....
So, the plane has a glitch or two... I'd still say it's a dang fine airplane, and if that's the worse of my glitches, I'm pretty happy.