Discussion about the Korg PolySix synthesizer

I finally got my klm-367 working again (it had been on the fritz ) and 
got the polysix all working and programmed  but noticed that when i set 
the three way modulation selector switch down to VCA  i suddenly heard 
a noticeable amount of white noise behind the desired sound. this white 
noise is also affected by the mod-rate knob so that when the knob set 
to any rate the noise pulses in the background when NO notes are played 
and is a bit annoying. the other 2 positions of that switch  vco and 
vcf  are quiet...no problems there ,  just the vca setting. any ideas? 
if i can clean that up its running at 100% after a year in the shop. ( 
perhaps  then time for that 'double your memory'  mod?)