No idea what is going on, but when we skype, other that the sound is absolutly crap on the other side (we hear the others fine, no issue, but they can barely hear us, very crackly and bits missing), there is this issue with the volume of capture going down automatically. Does that make sense? I don't touch it and you can just watch the slider of Alsamixer go down!
I just installed the latest version of Mint (Nadia? clean install), with the latest version of Skype that came with it. We had no issues with sound like this before the installation as far as I noticed. but it could have been, I don't skype that often. We did have suddenly issues with having to reset the volume every time we turned the computer on and issues with Nvidia. It would not reset the resolution to normal after we had changed it to use a data projector.
It's a Acer Aspire 9300