Only real possibilities are the connection from your audio card (or chip built-on the board), the wire itself, or the connection on the primary speaker (usually the single connection from the sound card into the left and then the right is connected through that). Only questions I'd have is "Is the sound coming from both speakers or only one of them?" and "Does the static/sound change when you jiggle the connection at the back of the speaker or the computer?"
As obob suggested, I'd replace the wire first (should be just a standard 1/8" plug) since that is the cheapest and easiest. I highly doubt it's the card itself if you're getting quality sound from the headphones. Might be the connection on the speaker side if the wire doesn't fix it.
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