Does the volume of the noise increase when you turn up the speakers? If so, the sound card could be picking it up. If not, your speakers are probably doing so. You can try taking the wireless card back and trying another brand.
Today I put in a wireless internet card, the internet works fine, but the card seems to be causing a problem with my audio device. When the wireless card is in my PC I get this odd static and screeching noise from my speakers/headphones. I know the wireless card is causing it because if I take it out the noise goes away. There are 3 open PCI slots between the two, I thought putting some space between them may help, but I was wrong, and I honestly have no idea what else to try. Any help would be greatly appreciated. Thanks!
If it matters, I'm running Winxp, the wireless card is Netgear wireless-g PCI adapter- WG311v3, and the audio device is a CMI8738/C3DX PCI Audio Device.