What is causing my speakers to have static and high pitched rings coming from them?

I have a Dell Optiplex GX1p with a Windows 2000 Professional OS. I installed an audio card and bought some speakers recently, but when I turn on my computer and the speakers, I hear weird static or fuzzy sounds, along with a less audible high pitched ringing. When I play music, they practically go away and are barely heard in the background. It seems to be only noticeable when sound is not playing. I have checked the connection of the card and the speakers, but I have no idea how to make the weird sound go away.