Hi think Vlc has a functionality or an option that doesn't work well with Realteck sound cards. When I use Vlc with Windows Xp, Windows 7 and even Ubuntu (every version I tested) I can not get a good audio quality.
Precisely: when I play an audio or video file at the beginning I can hear something like a whistle and sometimes there are other audio disturbs (the message log say: audio output is starving).
One of my friends has the same problem, he has a realteck sound card too.