Hi I have the latest 13" macbook pro with logic pro 9 installed and I plug my guitar into the jack port (switching the port to input). when I'm finished and want to listen to what I've done I switch the port round to output and plug my headphones in (yes I know it's a stupid way of doing it and I need a usb input). Problem is, when I switch it round, logic automatically switches to the built in microphone, and the built in speakers get insane feedback until I plug the headphones in. Then, When the headphones are plugged in the mic is still on and I can hear everything that moves on my desk. In fact as I am typing right now I can see the little input bar going up and down in logic. its really annoying This happens no matter what program I'm in or what track is selected on logic, so long as logic is still running. So can someone please tell me how to either turn off my mic, or set there to be no input to logic until I switch the jack to input and plug in. thanks in advance for your help!