I am no jet pilot but I am an engineer that has worked in the engineering department that designed jets.(F15,F16)
In my opinion Jr servos are set up to tight in the deadband. This means they will be very sensitive and jittery. Anything slightly wrong will set them off. It will not interfere with your flying but can make you paranoid.
One thing I would do is get rid of the NIMH pack and go to A123's. The lower internal resistance might help. If that dont help send them to JR and get them refurbished.
A regulator would likely make things worse.