Twitching problem

Hello all,
I have another problem for you guru's out there.
Started the 450 yesterday and was hovering about 4 foot of ground when i noticed the whole heli have this twitch/tick so bought it down checked the tail belt its fine, lifted again started again lowered down and watched tail with a bit of speed not twitching, changed gyro and servo just to be sure, started again today hovered again and the twitch is still there.
I have looked at all the wire connectors and speedie.
When its on the ground if i bring speed up to just before lift off, i let it sit there i can watch the twitch all the servos give a shudder when it happens.
I am running
ESC-tower pro h40 amp
Servo swash hxt 900
gyro turnigy 302
tail servo hk922
motor turnigy 2218
any one got ideas where it could be coming from?

Daza

For heading hold 63 down from 70.
tail is holding great nice and straight until it has this twitch and all the servos give a slight shudder.
Will try and video it tomorrow in day light see if that helps anyone.

It's not the old "slipping belt drive pulley on the shaft trick" is it?
The servos will twitch trying to compensate for slippage. The belt drive pulleys were notorious for this. Even though it was supposed to be fixed I still use green loctite on all mine before installing. There is not much holding them onto the shaft - you can just push them down the shaft with minimum force.

I have checked the tension on thebelt and retightened but still the same problem unless there is another slippage you are talking about. Still got me buggered never had this problem before i was thinking maybe something on motor or esc shorting out some where, but dont know if thats possible or not.

I have uploaded a video to see if that helps to work problems out.
its on you tube here.
http://youtu.be/Fc6Vo_GZhro

thanks all.