[Nomad84]

You don't by chance have a speaker connected to the microphone jack on accident, do you? In car audio, I've heard of people getting feedback when they run their sub amp off of the rear speaker signal. In particular, I've heard of people getting weird effects from the subs when they shut the trunk, which pushes the rear deck speakers up and results in a voltage on the speaker wire, which the amp sees, and plays back on the subs. It's possible that you have a similar effect going where one speaker (or more, probably) produces the sound and the other acts as a mic and pics it up, causing your computer to play it again. You should be able to check for this really easily by muting the microphone. Go to start-->run-->"sndvol32". You may have to go to Options-->Properties to get it to show the mic. Mute the mic and the line in and see if you still hear the echo. If so, it's something else and I probably can't help you :P