Sometimes the big silver knobs for Drive, Bass, Mid.... etc. including VOL...... get a little dusty/dirty and become very sensitive to the smallest vibration. This can cause the X3 to think that the knob has been moved, resulting in fluctuations of the affected setting.
Two things to recommend:
1) Move all of these knobs back and forth vigorously at least a dozen times; it will help clean/dislodge any dirt. If they seem really dirty you could apply some contact cleaner to the shaft.
2) when playing, 'park' all knobs (except Master Volume) to the far left - the zero position. This seems to be a sort of dead zone for the X3 sensitivity - it won't detect vibrations as movement so easily. Of course, after doing this you will have to change patches and then return in order to restore the last-saved preset settings.