I had something similar happen on the B string with one of my guitars. Only the B string buzzed at any position on the neck, including open. Through experimentation I resolved the issue completely. What worked for me was keeping the B string fine tuner screwed most (2/3 - 3/4) of the way down, thus exerting more force on the fine tuner tension plate. I usually prefer to keep all the fine tuners at the half way torqued down point, to maximize the plus or minus adjustment range. On this guitar the problem just disappeared when I adjusted that fine tuner down more than the others. Obviously I first unclamped the locking nut and adjusted the main tuners to compensate for this action.