Hi keithv,

I just discover your post right now.

I do not see any writings about the RC integrator circuit which should take place between your CCP1 output and the audio input. This RC network eliminates most your sampling signals.

In my application I use R = 1k and C = 47nF for a sampling rate of 56 kHz and this works fine.
You should modify the values accordingly, for example C should be about 120 nF for a sampling rate of 20 kHz.

Best regards
MikeBZH