Have you checked the BEC voltage on the ESC? I've noticed when I put mine on 7.4 the steering servo is a little nervous and sings to me. I'm installing a glitch buster but that won't be until I get back from vacation in 12 days or I'd let you know how that works out. In case you're wondering a glitch buster is a capacitor that plugs into an unused channel on the receiver and is supposed to smooth out the power to stop the twitching.