RE: QUESTION ??????
Well... one explanations may be that there is a short in the antenna wire, or somewhere on the surface mounted hardware (electronics) you have a small crack in a circuit. I have two 120's and both of them run a little different. I would try taking the electronics out of the one that glitches and swapping them out. If this process of elimination works then you will have your answer. If not, the only explanations I can give is the resistor on the motor may be bad