[digitalradio] RF feedback problems

[David Bowman WB0QIR]

I have a Kenwood TS-680S rig and am using a psk31/rtty soundcard
interface from Associated Radio.  Whenever The db9 data cable from the
interface is plugged into a computer my signal is terrible when I
transmit data or use the microphone.  Unhooking the microphone does
not help.  Before I buy some ferrite chokes I wanted to see if anyone
has any other ideas of how or what the problem may be and how to fix it.