Could be a lot of things :
How much memory do you have.
Is this an usb soundcard , or an old pci pc 128 sound card .
Is there an irq sharing with the soundcard .
In order to get good sound trhere\'s the quality of the card ,the quality of the speakers , can depend on the pci slot , not enough memory , cabling , conflicts with drivers of other cards , or it\'s own drivers , interference , etc....
If it\'s a new pc you buyed it has to be functioning properly .