I have noticed the same thing Dick, each servo, when plugged in progressively reduces the range.
After the set is turned on, if you let it sit for a few seconds, it will quit buzzing and eventually quiet down until you move one of the joysticks and then it starts the buzzing all over again. There is little doubt in my mind that the linear wire wound resistors used for the feedback pot in the servos contribute to this problem. I added a tantalum 100uF cap across the 4.8 volt traces of one servo and that quiets it down considerably, but does not cure it altogether. Due to the constant buzzing (servo hunting) it drains the batteries pretty quickly.
Jay