That sounds like you are picking up electrical noise (spark noise or whine and white noise from the alternator) from the bike. The usual cure is to use isolated cables on the audio and occasionally, the power side of the Starcom.
Mine does not use a power input isolated cable but I am using the standard Starcom audio cables, which are isolated I believe.
The C-14 is a pretty 'quiet' bike electrically because of the stick coils; there is no high voltage anywhere outside the engine (except maybe right on top of the valve cover) so there is little risk of picking up ignition noise. You might have alternator noise in the Starcom though. There are a few methods to try and reduce that: do not run any wires to / from the Starcom next to any of the bike's harness wires, and especially not with the wires coming from the alternator. When crossing other wires with the Starcom cables, try to do it as close to 90 degrees as possible; this will reduce the induction in the Starcom's wiring. You might have to simply re-wire the Starcom, starting with the 12 volt power wires, and see if you can eliminate the noise you are now picking up.
Brian
Good and bad news.
With each circuit and the engine off, the audio improves a lot.
But with the engine on and idling in the garage, the audio is so bad I can't hear myself talking using a 1866.... Test phone number. Plug the Starcom1 MIC-02 cable back in and the audio is back to current state.
This is beyond my talents...I'm not happy.