How to prevent my Steam from messing with my outside audio?

This is a windows feature which can cause issues with a number of gaming applications e.g. Steam and Teamspeak. Fortunately there's an easy way to turn it off:

  1. Go to your Windows Control Panel
  2. Sound
  3. Communications tab
  4. Where it says "When Windows detects communications activity:", Select "Do Nothing"

Do nothing

Windows automatically partially mutes other applications when it detects what it thinks of as a phone call.