Thanks guys i'll try the power capacitor.
I just tried removing the bullet connectors esc/motor and solder directly to the motor... Not that ....
Can i use the power capacitor of a Novak GTX ?
I'm not a Novak employee but I've used lots of their motors. I had one motor replaced under warrenty when it was doing this.
The cogging would be cause by the sensor and the power being out of phase with each other. It could be in the motor, the sensor wire or the ESC. You say you've tried two motors with the existing GTB. Now try those motors with a different GTB. That way you tell if its the motor or the ESC.
The power capacitor should not be the cause. It only smooths out the power from the battery to the esc. You can run without it but you just don't have as much punch. Its more noticable with mod motors.