i have an Ibanez SZ320... the Rhythm pickup knob is loose, it still works but its getting looser, ive been told to open the back panel and tighten a nut/screw/whatever, trouble is I can't see one.

anyone know what to do other than bring it into a shop?
Ibanez SZ 320
Ibanez Strat - old Ibanez logo, signed by Mark Morton and John Campbell of Lamb of God
Vox Wah Pedal
30 watt Line 6 Spider 2
and a shitload of picks