Ga-8st800 Onboard Card Problem?

I have a small problem with the sound on my GA-8ST800 mobo, i've win x
now and the CD-in cable disconected but when i turn up-down the c
volume from windows program I hear a zip sound, it also sounds whe
turn up/down the master volume from windows program. At the beginning
thougth it was the windows, so i installed win 98 and the proble
remained. When i mute the cd volume the master volume stops the zi
sound at up/down volume. Is it a hardware problem or it is a bug on th
mobo? Has anyone encountered the same problem any time? I had a
accident recently (a usb connector installed at wrong side and the PS
was burn out, the mobo after that worked but i don't remember if th
problem mentioned above was before or not. Does anyone has any idea wh
is that sound heard?(At win98 the cd-in works perfect i hear clear soun
of the cd audio but changing it's volume it makes a sound like
zipper)
Thank you in advanc