I can not find jack plug on this audio board. @kalin, could anyone check it? Thanks.

2 boards show this failure:
chromeos15-audiobox8-host2
chromeos15-row13b-rack3-host8

I am sure audio box at chromeos15-audiobox8-host2 has plugger, but I know for at least 2 boxes we had to not use the plugger, as always plugged setup delivered better results. Yes, it looks like this is one of them:
10/07 11:48:33.205 WARNI|       audio_board:0035| There is no jack plugger on this audio board.

We have to check manually pyro board for audio jack node(s).
Matt, can you re-test if nodes(esp. MIC) are affected when hotplugging audiojack 3.5mm  headphones?

On second look, all milestones builds started failing. from relatively same time, so it does look more like test bed issue. 

AI_1: manually test pyro board
AI_2: check test beds for obvious issues, re-set both hosts audio connections, restart chameleon, and re-run test

Re: #3 - 
AI_1: Tested manually on Pyro with build version 71.0.3567.0/11137.0.0 and do not see any issues with External Mic

AI_2: Will file a bug for lab team to check.  

Filed b/117431626 for AI_2 above

Thanks Prasanthi,
lets wait and see status after lab team re-sets hosts.

Results below for the tests after re-seating the audio cables on the above hosts that were regressions since 10/03:

audio_InternalCardNodes	                Test is now passing
audio_AudioAfterSuspend.external_mic	Test is now passing
 
audio_AudioAfterReboot.external_mic	Test is now flaky 
audio_AudioAfterReboot.headphone	Test is now flaky 

audio_AudioBasicExternalMicrophone	Test is still failing

What was the status of these tests before this bug was filed?

All the tests were passing earlier.
Screenshot: https://screenshot.googleplex.com/2NQwut46t1Y

Per Kalin: 
1. Made sure that there is no HDMI & USB connections between Chameleon and DUT.
2. Only audio cable is connected
3. Rebooted Chameleon and DUT's and able to ping and ssh to all on the above hosts.

Ran this test 'audio_AudioBasicExternalMicrophone' locally on chromeos15-13b-3-8 and the test is now passing.  

16:15:46 INFO | autoserv| Starting master ssh connection '/usr/bin/ssh -a -x -N -o ControlMaster=yes -o ControlPath=/tmp/_autotmp_jVyuZ6ssh-master/socket -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o BatchMode=yes -o ConnectTimeout=30 -o ServerAliveInterval=900 -o ServerAliveCountMax=3 -o ConnectionAttempts=4 -o Protocol=2 -l root -p 22 chromeos15-row13b-rack3-host8-chameleon'
16:15:51 INFO | autoserv| Timed out waiting for master-ssh connection to be established.
-------------------------------------------------------------------------------------------------------------------------
/tmp/test_that_results_ldoHuM/results-1-audio_AudioBasicExternalMicrophone                                    [  PASSED  ]
/tmp/test_that_results_ldoHuM/results-1-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone [  PASSED  ]
-------------------------------------------------------------------------------------------------------------------------
Total PASS: 2/2 (100%)


Same test in audiobox seems to be failing: will look into it further and update later

16:36:15 INFO | autoserv| Starting master ssh connection '/usr/bin/ssh -a -x -N -o ControlMaster=yes -o ControlPath=/tmp/_autotmp_agVWxzssh-master/socket -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o BatchMode=yes -o ConnectTimeout=30 -o ServerAliveInterval=900 -o ServerAliveCountMax=3 -o ConnectionAttempts=4 -o Protocol=2 -l root -p 22 chromeos15-audiobox8-host2-chameleon'
16:36:20 INFO | autoserv| Timed out waiting for master-ssh connection to be established.
16:36:28 INFO | autoserv| rsync not available on remote host chromeos15-audiobox8-host2-chameleon -- disabled
-------------------------------------------------------------------------------------------------------------------------
/tmp/test_that_results_drAQPr/results-1-audio_AudioBasicExternalMicrophone                                    [  FAILED  ]
/tmp/test_that_results_drAQPr/results-1-audio_AudioBasicExternalMicrophone                                      FAIL: ['INTERNAL_MIC'] rather than external mic is selected on Cros device
/tmp/test_that_results_drAQPr/results-1-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone [  FAILED  ]
/tmp/test_that_results_drAQPr/results-1-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone   FAIL: ['INTERNAL_MIC'] rather than external mic is selected on Cros device
/tmp/test_that_results_drAQPr/results-1-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone   10/09 16:28:15.835 ERROR|             utils:0283| [stderr] Warning: Permanently added 'chromeos15-audiobox8-host2-chameleon,100.90.15.167' (ECDSA) to the list of known hosts.
/tmp/test_that_results_drAQPr/results-2-audio_AudioBasicExternalMicrophone                                    [  FAILED  ]
/tmp/test_that_results_drAQPr/results-2-audio_AudioBasicExternalMicrophone                                      FAIL: ['INTERNAL_MIC'] rather than external mic is selected on Cros device
/tmp/test_that_results_drAQPr/results-2-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone [  FAILED  ]
/tmp/test_that_results_drAQPr/results-2-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone   FAIL: ['INTERNAL_MIC'] rather than external mic is selected on Cros device
/tmp/test_that_results_drAQPr/results-2-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone   10/09 16:31:28.726 ERROR|             utils:0283| [stderr] Warning: Permanently added 'chromeos15-audiobox8-host2-chameleon,100.90.15.167' (ECDSA) to the list of known hosts.
/tmp/test_that_results_drAQPr/results-3-audio_AudioBasicExternalMicrophone                                    [  FAILED  ]
/tmp/test_that_results_drAQPr/results-3-audio_AudioBasicExternalMicrophone                                      FAIL: ['INTERNAL_MIC'] rather than external mic is selected on Cros device
/tmp/test_that_results_drAQPr/results-3-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone [  FAILED  ]
/tmp/test_that_results_drAQPr/results-3-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone   FAIL: ['INTERNAL_MIC'] rather than external mic is selected on Cros device
/tmp/test_that_results_drAQPr/results-3-audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone   10/09 16:34:47.793 ERROR|             utils:0283| [stderr] Warning: Permanently added 'chromeos15-audiobox8-host2-chameleon,100.90.15.167' (ECDSA) to the list of known hosts.
-------------------------------------------------------------------------------------------------------------------------
Total PASS: 0/6 (0%)

Re: Update to #10 - There was a USB cable connected between DUT & Chameleon which I removed it yesterday on host chromeos15-row13b-rack3-host8 

All the regression issue tests are passing now.  
Screenshot: https://screenshot.googleplex.com/pwODcm5Z8tS

Thanks Prasanthi.
Marking as Fixed

Marking as verified.  
Screenshot: https://screenshot.googleplex.com/41fu95C7A09