I added 0.1 uF caps between pin 7 and ground, +12 and ground and PTT and ground with no improvement to the buzz noise on tx.
I put resistors in line of the +12 to the mini board, and found that the mute did not function above 3.3k. The mute did function at 390 ohm and there was a delay of a second or two before the buzz started.
So no real improvement yet.
I can fix the buzz problem with a relay, which may also fix the keyup pop after transmit.
The unstable frequency on transmit is a bigger problem so I will shift my attention to that. Any ideas for what to try?