Casio CZ/ VZ/ FZ - Pro Series

Hello everyone, this is my first post.

I recently bought a very nice and full functioning CZ-3000 through Craigslist and so far I'm having a blast with it.  I've always had Casiotones around but have been until recently unaware that Casio made "real" synthesizers.  

Anyway, I've noticed that on the clean-sounding presets (Elec Piano, Vibraphone, Fairy Tale, etc.) there is a low level distortion, or background fuzz, as if the signal is clipping or overdriving.  This happens at lower volumes as well.  It's not that loud but it definitely is noticeable.  At first I wondered if it was just my machine then it occurred to me that the distortion may be a product of Casio's phase distortion synthesis.

Over at Synthmania, the same distortion can be heard on the aforementioned presets:

http://www.synthmania.com/cz-1000.htm

This leads me to believe that maybe the synth just has a bit of noise on cleaner, clearer patches, an inevitable byproduct of PD.  Or maybe the CZ-1000 at Synthmania also suffers a common issue.

Any information would be much appreciated!  

Thanks,
Parker