All about the Roland Jupiter-series

Hi there!

I've had my Jupiter 6 for nearly four years now - and have recently 
noticed a problem that perked my ears up. (I know this might be a bit 
of a "dumb" question, but I'll post it anyway).

On every sixth note I play, only one oscillator sounds - well almost. 
If I turn the mixer knob to VCO 2, there is a faint sound - but quite 
low. Almost as if the ocsillator is still functioning, but the 
amplification has been lowered significantly. I can get full volume 
on the noise waveform though - strange, huh?

Is this a common problem among JP-6's?  Anyone ever experienced this 
phenomenon before? 

Any help is appreciated! I just wanted to ask before I took it to a 
repair shop.