My MIM Fretless jazz gets a strange "woof woof woof" sound on notes above the 12th fret on the E string. It's like an out of phase vibrato. (I'm not sure if I'm describing this right). In any case, it's not a clear note like the other places on the neck or on other strings. I'm using TI Jazz Flats. It does the same thing with roundwounds, but not nearly as pronounced. Any suggestions?