Computer speakers with '電視雪花聲', help...

1. 電視雪花聲 comes out from both speakers of the monitor. The computer plays music as usual, but 雪花聲 is still heard at the same time. The sound increases as the volume increases. When I plug external speakers to the computer, the effect is the same. What's going on with my computer? Sound card problem?

2. How much do I need to pay to fix the problem? It is a desktop - Sony, Vaio PCV-L640.