Just acquired a 72 P-Bass which I love, BUT, when I play the E on the 9th fret of G string it causes a continuing hum even after I mute the string. Annoying because it causes dissonance with other notes. I finally realized the hum goes away when I mute ALL my strings, because what's happening is that the other strings are vibrating. Any thoughts on why this is happening? Not an issue with any other notes as far as I can tell.