I recently restrung my Ibanez EDB600, which I've had now for about 7 years. Almost immediately I notice that both the E and A string emit a weird chorus-like tone (amped or not) that intensifies the further up the neck I play. After the twelfth fret or so, the sound is pretty much unbearable. So what did I do? I adjusted the truss rod, the saddles, the pickups, and put on a brand new set of strings. Still the same problem. I'm going nuts trying to figure this out!