I've got some issues with my headset. Namely, it seems, that my system (Ubuntu 12.10) records sound not from a headset's microphone, but from what I hear in the headphones. For example, I can plug in the headset, turn one the music on my PC and the system will treat this music as a sound input. It happens even if I set volume to 0. This issue have started to bother me recently. Before that time everything worked OK. And the matter is in the system, because I've tried 2 different headsets (one of which was completely new) and both of them encountered the same problem.
So, can anyone give me a piece of advice of what should I do?