Asus p5b Sound problems

I have had my Asus P5b for a long time now and i have had this problem before but i cant fix it in the same way i did last time. the mother board has a built in sound card and it was working with no problems. I recently installed a new graphics card (9500 GT). the graphics work but i lost my sound. at first it was completely dead, no sound at all, and i tried updating the sound driver software, but i was already at the newest version. the speakers and cords are good, i tried them on another computer. i also went to the Asus website and installed the newest audio driver from there. it's called SoundMax Audio. now the speakers only give out a static sound that seems to increase with the more activity i have on my computer (like opening websites or playing games). someone please help me out, I CANT TAKE ANY MORE OF THE HISSING!!!!