The volume of my Pioneer DDJ SX increases and low suddenly

I use Pioneer DDJ SX with serato 1.9.2, when i am playing music, passing some minutes Main master volume increases and low without suddenly.

Another problem is on knob effects channel 3, playing music on channel 3 the effect active itself, and to undo the effect have to turn the knob to right side as if to activate the effect when I'm looking for the point where the effect = 0db.

I need help, already tried to investigate similar problems on the Internet not found.

NB: I'm using the last firmeware the pioneer for DDJ SX