I bought a new xdj xz.  Love it so far but there is a weird sticky residue on the main knob for browsing tracks.  Ive taken it off and cleaned it with soap and water and it doesnt seem to go away leading me to believe there is something wrong with the knob's plastic.  After using the knob I can feel a tacky substance on my finger.  Washing the knob helped for a bit but the issue is still there.  Has anyone else ran into this issue?