I have been running Linux Mint 9 on a Dell Vostro 1220 netbook and cannot seem to find a way of resolving the following problem. Any suggestions or links much appreciated.

Overall this OS runs excellently on this machine, but there is a bug (or required config) which keeps the built-in microphone and speaker from switching off when the external audio and mic jack are being used.

It is weird since I imagined it would be a physical switch that disconnects the built-in mic and speaker, regardless of OS. All works well for Windows 7 (dual boot) but not Mint 9 (I have not tried any other OS yet).

I noticed this issue whilst speaking into the mic on my first Skype call and the other person could not hear me properly, and I discovered it was because I was quite a distance from the built-in mic. So the external mic does not work, but the external speakers does work simultaneously with the built-in speaker, therefore the sound image is confusingly somewhere halfway between the external speaker and the netbook.

Hope someone may know how to fix this odd issue.