This use to be a real common thing in on-board sound (At least in the brands I have used, was one of the reasons I insisted on Soundblaster (usually 16's) cards in systems I built). The solution is to turn the gain down in the controls and the volume up on the speakers. It has been a while since I have seen one with that problem, but it also use to do it with el-cheapo cards (a few years back).