[Elecraft] K3 MON feedback question

[K5WA]

I thought I knew my K3s pretty well but I've got a simple issue that I can't
seem to figure out so I thought I would toss it out to the crowd to see if
you can clear my fog.  There must be a simple setting that I've set
incorrectly.  I don't get on SSB very often but I'm trying to get ready for
CQWW SSB soon and needed to go through this process of setting up the PC
sound card for sending recorded messages.

 

Problem:  I can't use the MON on SSB because I get feedback (not the
squealing type but the RF garbled sounding type) into my transmitted signal.
When MON is set to zero, everything transmits perfectly, but, of course, I
can't monitor my audio.

 

Setup: Pair of K3s in SO2R with homebrew SO2R switching box.  (The problem
occurs with or without the SO2R box installed.)  I use LINE IN  for my
recorded messages and my MIC is attached to the rear MIC input.  My
headphones are connected to the rear PHONES jack via the SO2R box.  Sound
card is the internal PC sound card of a DELL XP machine.  MIC+LIN = ON. FW
4.06.  KDVR3 installed but not used for contests.  KRX3 installed but not
involved in this problem (I don't think).

 

It seems as if my headset microphone is picking up audio from the MON and
dumping it into the MIC line, however, the speakers are OFF and I'm only
using headphones.  Since it can't be the speakers, I'm thinking I've got an
open path between the MON and the MIC input but I'm not sure where that
could be...inside the K3, on the PC sound card, etc.?  

 

I'm hoping to hear a simple "Did you set your so-and-so to OFF?" suggestion
that will trigger an Ah-ha moment for me.  I know it isn't a "pin 1" problem
because that went away when my microHAM MK2R box got hit by lightning last
month.  ;-)   Maybe my sound card is hearing the MON and dumping it back
into the MIC inside the PC?  I'm not sure whether the sound card is full
duplex or not.  Any suggestions would be appreciated because I'm stumped and
would appreciate a new set of eyes on this issue.  

 

Thanks,

Bob K5WA