Sound problem (Stereo cancelation)

[Loke1]

I have a problem with the sound on my troublesome computer. A sound played both at right and left channel get a tincan sound, very veak or gone, but sounds played in either left or right is OK. So lead singer and such dissapear.

I noticed this problem while loading a *game*
I have not configured suround, only stereo, and never had this problem before. I did not tune anything before this happend. I have a sound effect manager from VIA, and a soundcard from VIA.

Hope someone can help me with this.