waveshark

hi i have a hitec radio system in my boat and i am having a problem with the steering servo the servo will wiggle and make steering impossible. it is alright if i give it full right or left but inbetween it jumps around everywhere. i switched the servo to the throttle position and it worked perfectly. beleiving it was the receiver i tried my other hitec receiver and it did the exact same thing and worked perfectly in the throttle position. so i finally tried my brothers exact same transmitter as mine and the samething occured. so i cant narrow it down to the transmitter or receiver. has anyone got any ideas. the only thing i used in both receivers on the test was the battery pack. any help would be greatly appreciated. i thought maybe it was the battery pack supplying not enough voltage?
Thanks Tom