Sorry it took me so long to get back to you on this.
As jzucker said, it is truncation noise/distortion. You bit reduce a signal by truncating the sample to a specific number of bits.
If you are running the latest beta version of software, the background noise when you are not playing should be gone. Let me know if that isn't
The bigger question is, what were you guys expecting/hoping to hear at 14 bits that you are not, and how can we improve it to help you guys out. I obviously can't promise that we can or will do everything. But I'd like to try.
For what it's worth, I am the DSP engineer that designed and coded the sounds for this product, so the software guys are looking into it.