All about the Roland Jupiter-series

Hello,I have been using my Jupiter for 3 years without problems but 
now I'm not sure wether or not this is normal : 
When I have a string-pad and I use UNISON-mode the right output of 
my JUP8 sounds distorted....Not all my sounds do this,just some 
sounds.(Most with the VCA wide open)
Could it be possible that when I have a sound with VCA full open and 
UNISON activated that the right output distorts?
Is this normal?

Thanxxxx