Your mic settings are wrong for the Mixer. If you did everything in the advdemo.exe, then, there is something wrong. Here is a suggestion, mute your mic when not in use OR slide the mic slider down to 0. If the listeners still pick up your mic noices, I suggest getting another mic or, using linein, get your own mixer panel and broadcast your own stream from something like a DJ turntable or something.
Developer; On-Demand Audio
Yeah, that's pretty much it. :-\