Since this came up twice recently:
1) Turn BIAS all way CCW
2) Remove knob
3) Turn shaft of pot until audio barely audible. Back it down
ever-so-slightly
4) Re-attach knob. Tighten knob so pointer line is at 0.
Note: this may "skew" the knob CW or CCW (ie all the way CW not to 1.2 tick)
That's OK!
Paul S.