The ESC gets its power form the battery, not the RX. Sounds like your receiver has a short in it that causes a jolt in the position signal for ESC when the servo initiates movement. What type of RX and how old? How well has it been treated?

What type of chassis is this set-up intalled in? If it is Carbon-Fiber, or even carbon reinforced, it may be power wire contact or even antenna contact with the chassis...