That sounds like a shift flare which the trans will do to make a smooth shift. I'll get what sounds like happens to you around 30 mph if I'm on the accelerator slightly then back off ever so slightly.
You don't "anticipate" shifts and let of so it will. I have this ******** habit, don't it forever, in my mind, i think it takes the load off of the tranny so discs slip is minimized. However if i understand this transmission correctly this is stupid because i believe its almost like the dual clutch manual, in other words , nothing unlocks until its locked into the next gear, always contact in other words. Not sure.
Any way i swear mine does this sometimes, or was it one of those in my mind sort of things.
One more thing, this flare thing, would it possibly be the thing it does when your cruising in high gear and say go over a small hump, let off the trottle ever so slightly, the rpms bump couple of hundred, get back on the gas they go back. Told this is normal as the torque converter is unlocking for that moment to i guess eliminate dynamic braking, or drag. Like pushing the clutch in on manual and letting out.