well dude i had a pretty similar problem offlate like u have mine was Sis Chipset....
Well unfortunately onboard soundcard sometimes just goes bizarre and doesn't work.. i also believe that u might have heard a few click sounds that is it...
I assume that there are no sounds whatso ever in ur computer...
Except the click sounds and those few winamp sounds...
There is no problem as such with the connection ... i am also sure .. the simple old solution following (KISS) Keep it Simple and Safe.... go 4 a PCI slot sound card ...
i have gone for a crystal make which is dirt cheap ok ..
and i am sure this shud solve ur problem b'coz PCI behaves differently...