I decided to follow hellsfury_25m advice and updated the driver of the motherboard sound card. This solved the problem, it was not a deffect in the motherboard but the drivers that came in the CD.
My Motherboard is a Magic Pro P6PE-1000
I found the source of the problem. It seems that came from the motherboard integrated sound card (or the driver as hellsfury_25m sugested). I disabilitated it and replaced it with a full duplex sound card and the problem was gone.
Thanks guys.