I watched the video again...actually 2 more times and now Im not quite certain.  Thanks morgan for making me doubt myself!  LOL

It does sound like the motor is losing power for a millisecond and recovering.  But maybe the sound I am basing that off of is just the less resistance on the tail rotor when this "glitch" happens...thus making it sound like the motor.

Mabye it is a bad servo/gyro.  Do you have another servo to change out and check?

Unlike morgan...I only have a nice cache' of spare parts for my 450.  I really have hardly ANY spares for any of my other helis.  I need to work on that!  But, I have enough 450 spare parts to rebuild from a crash several times.  Probably have TOO many parts for the 450 and not nearly enough(none) for the others in my fleet!