Line-in static?

I have a keyboard, which I run through the line-in port in the back of my computer. There is static coming from my speakers when I unmute the line-in port, but when I mute the port, the static goes away. I've done some research on it, and it's not a ground loop. Also, the output from my keyboard works fine whenever its plugged into anything else.

It would probably be best to mention that a little while back, I accidentally shorted out my onboard audio. I am now running off of a pci audio card.

http://www.newegg.com/Product/Prod [...] 6829186003
Nothing is plugged into the mobo audio ports or front case ports.

It's hard to accurately describe the static I'm hearing-it's like white noise, combined with random beeps.