Ok, so,

I have an aux line plugged into the line-in on my computer. When I plug it into the microphone jack (causing the input to be played through the speakers) it sounds perfectly clear (thus, there's no problem with the line). But when I record it and play it back, it sounds echoey and the background buzz is significantly louder than what I'm actually recording. I've recorded before with a line-in to the microphone jack (from my guitar) with no such problem. Also something I find odd is the input source selection box in audacity (right next to the input volume slider) is greyed out. Anyone have an idea what's wrong?