Discussion about the Korg PolySix synthesizer

Is it normal for Trident and P6 to be noisy ??

Both of mine are very noisy, particullay the synth section on the 
Trident, and the P6 synth. Sounds like bad earth (I know there's no 
ground problem in my apartment).

Listening by headphones, the noise is very noticeable, and even a bit 
distorted sometimes in the synth section on my Trident.

Any idea ? (BTW I installed a MIDI retrofit in the P6 and started 
making inside wiring of the one for Trident)