I'm going to assume that all your drivers are up to date but first things first. It sounds like your experiencing a lot of static on your onboard, guessing you can hear it when audio is playing, and I'm not sure the level your experiencing it on your pci card. Now generally there are two sliders on your sound control with one being volume control and the other being wave. If for whatever reason you have these cranked up, that will produce more static seeing as how more power is flowing through the card. It is possible that your onboard is defunct and try to play around with the setting on each card and see what you can find.