Today I noticed something that has happened to me before in the past but when I was using Windows Vista (I'm now on Windows 8). Basically, when I join a Skype call, everybody can hear the sound I'm playing through my PC, for example; a song in iTunes. They can also hear themselves echoing through my mic and they can hear any youtube vids I go on etc. I have no idea why this is happening but I think I remember it being something to do with stereo mix. Windows 8 has no stereo mix option, if anybody can help me I'd really appreciate it.
I've messed around with settings on both recording and playback devices, I've tried 2 different headsets and done multiple restarts, nothing is fixing it.