#4 From fine to "What the...!"
 

I don't know if anyone has had this happen yet, but it happened to me today. I was practicing hovering my #4 and noticed it kept wanting to spin left and I kept hearing the tail motor cycling from stable to full. Trimming didn't seem to help. Needless to say it was a handful to control. I had it up the other day and would hover fine. Well, I kept messing with it and finally had a tail strike and threw a tail rotor bearing in the grass[X(] What a bear to find that! Any how, I checked the helo and noticed the receiver was loose, meaning the tape was letting go. The receiver was canted to the left and was most likely shaking back and forth with the vibes and throwing off the gyro. Which is probably why the rudder was cycling. Just wondering if anyone had experienced this before.

RE: #4 From fine to "What the...!"
 

The tail will also spin up or slow down randomly when it's near it's own demise. I had the same problem, with the tail cutting out randomly during flight and swinging, and then go back to normal like nothing happened. After a few flights like that, the motor stopped working alltogether [:'(]

Although, if your receiver was loose, that would account for it aswell ;)