When you tap the fuse, is your radio on? If not, it is not uncommon for servos to chatter when the radio is off.

If it was on, it sounds like you have a loose antenna, or the antenna is resting against something that is generating interference.

GWS receivers have very limited range. The 4 Ch pico is about 500 feet so you could have gotten out of range. They are also not known for glitch free perfromance, but you sound like you have a different problem.

Did you range check it? How far? No problems? With motor on and off?