K3, noise during SSB TX

[wa9fvp]

Working with Craig at Elecraft, we determined that the TX noise was caused by the MON turned on in SSB mode.  I'm trying to understand what's causing the noise. The feed back path for the monitor would have to be internal to the DSP software.  That is the mic audio A-D would have to be mixed with the speaker's audio D-A converter. For some reason the mix is causing a high level of digital noise that's fed to a third D-A (the output that feeds the TX/IF).   Any thoughts from a DSP guru?

Jack WA9FVP
Willco Electronics.