can you confirm is this happen on Chrome browser only? It doesn't sounds like a chrome media bug. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c57ee457bd68b3df962dc3b109fc0535e83be502

commit c57ee457bd68b3df962dc3b109fc0535e83be502
Author: Guido Urdaneta <guidou@chromium.org>
Date: Thu Dec 07 20:14:10 2017

Improve audio-device monitoring on Mac

Before this CL, base::SystemMonitor on Mac only reported addition and
removal of input devices.

With this patch, the following events are reported:
* Addition and removal of output-only devices.
* Changes to the default input or output device.

With this change, it is safe to enable the SYSTEM_MONITOR caching
policy for MediaDevicesManager.

Bug: 788687,  648173 
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I57549eb586716a3739d652c386f7740875521be8
Reviewed-on: https://chromium-review.googlesource.com/803218
Reviewed-by: Max Morin <maxmorin@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522524}
[modify] https://crrev.com/c57ee457bd68b3df962dc3b109fc0535e83be502/content/public/common/content_features.cc
[modify] https://crrev.com/c57ee457bd68b3df962dc3b109fc0535e83be502/media/audio/mac/audio_device_listener_mac.cc
[modify] https://crrev.com/c57ee457bd68b3df962dc3b109fc0535e83be502/media/audio/mac/audio_device_listener_mac.h
[modify] https://crrev.com/c57ee457bd68b3df962dc3b109fc0535e83be502/media/audio/mac/audio_device_listener_mac_unittest.cc
[modify] https://crrev.com/c57ee457bd68b3df962dc3b109fc0535e83be502/media/device_monitors/device_monitor_mac.h
[modify] https://crrev.com/c57ee457bd68b3df962dc3b109fc0535e83be502/media/device_monitors/device_monitor_mac.mm

 Issue 678466  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0712d9513ba17d569d6f96b07c8f7d0abaa1796f

commit 0712d9513ba17d569d6f96b07c8f7d0abaa1796f
Author: Guido Urdaneta <guidou@chromium.org>
Date: Fri Jan 12 16:30:38 2018

Allow default caching policy for MediaDevicesManager on Mac.

This CL removes forcing the NO_CACHE policy for output devices
on Mac. The reason is that a fix for the Mac device monitor has
already landed.

Bug:  648173 
Change-Id: I2b2226c2a5e65f706aff7b21360700f1fc04b2f2
Reviewed-on: https://chromium-review.googlesource.com/860412
Reviewed-by: Max Morin <maxmorin@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528963}
[modify] https://crrev.com/0712d9513ba17d569d6f96b07c8f7d0abaa1796f/content/browser/renderer_host/media/media_devices_manager.cc