Well my Strat was behaving like that last week. When I touched the metal on the jack the noise was gone. Turns out the ground connection from the bridge to the electronics is at the back of the guitar, at the steel plate which holds the strings to the guitar body had come loose. They soldered it directly to the chrome which is sure fire way to have it disconnect later. I ground the chrome with my dremel and soldered the ground lead to the underlying iron, now you can yank it at will and the noise is gone.