HELP!

I'm using a Castle Creations 25 amp ESC in an Alfa F-86. I've tried several different brands/models of receivers and with all I'm getting severe interference, e.g., servos jumping around, ESC pulsing the motor RPM up and down; the problem seems to be worse at certain RPMs. Even without the motor running, the servos jump around when the ESC arms, e.g., when it chirps. I tried a ferrite ring on the end of the ESC control wire, but it didn't help. I'm lost! [&:] Any ideas?!?

Thanks

/pem