Hi Dan,
The Baofang UV-5 radios are finicky, because the Tx and Rx "serial port" lines are shared wtih the audio (mic in and sp out) lines.
Unless I am misunderstanding what you are saying here, they are not shared. Only the TX data, RX data and ground wires are in a 2-pin Kenwood style programming cable. The speaker and microphone wires are left out because they are not needed for cloning. The pinouts of the 2-pin Kenwood style speaker/mic plug can be seen here.
http://www.miklor.com/COM/UV_Technical.php#spkrmic
It would be great if they were shared. We could then buy cheap $3 programming cables and cut off the USB end to make cables for APRS and other projects that need to have speaker and/or mic audio from the radio.
Therefore, it is essential that you tune the radio to an unused RF channel and trun the volume all the way up to 100%
I have Baofeng, BTech, Retevis, Kenwood, KDC etc. radios (various models of most) that use the 2-pin Kenwood style programming cable. In the 7 years I have been programming these radios with a computer, I have never intentionally turned the volume up any higher than the "click" it takes to power each radio on (unfortunately I let someone talk me into putting it into the cloning instructions for the uv5r driver).
I have also never had an issue programming a radio with CHIRP when the radio is tuned to a busy channel. For example I just downloaded from and uploaded to my UV-82 while tuned to the local NOAA WX Radio frequency which is busy 24/7. It is worth noting that some of these Chinese manufactured radios cannot manually program a memory if the VFO is tuned to a busy channel.
I do recommend that the radio is tuned to an unused frequency when programming, though. The reason is because there are several ways that an improperly configured and/or improperly connected programming cable can cause the radio to transmit (which would cause interference to the users of a busy frequency).
Jim KC9HI