Casio CZ/ VZ/ FZ - Pro Series

hey all- i recently bought a CZ-1000 fairly cheap, but it seems there 
is a constant hum/buzz from the headphone jack. The hum stays at the 
same level with the Vol high or low. The output jack is clean and 
sounds great, and every thing else works perfect. Just wondering if 
this is a common problem and an easy fix--worth taking the unit apart.
 Or should i just leave it be and live with it??
   I'd rather not have to run the output line through a mixer into 
phones(late night sessions) every single time i want to write. And 
believe me,after an hour of dealing with that buzz in the phones my 
brain starts melting out my nose!!
  Any help would surely be appreciated.  -Thanks!!!
                                                   -cb