Do you know anyone who has an oscilloscope or signal analyzer of some type? I'd want to check the BEC output, see if it has unusual noise / voltage fluctuations, as the ESC is worked some.

Perhaps some wild speculation, but notice how many digital servos tend to have some chatter or noise or whatever? What if the BEC has noise at the same frequency, that might give the servo some issues, make it work harder in a sense?

when using the esc the servo made some intermittent noise, but i think its normal since its a digital servo. I think let this be a lesson in the future to those reading this so as not to assume its always the rx fault.

Good point. I have a couple of digital servos that vibrate sometimes off load and also make a continuous hum. Sanwa put this note on their website as 'normal operation' so I don't worry but it is a phenomena that seems prevalent in digital servos!