Is this noise (static hissing sound) on when you play music..or other applications?
Does this noise occur with everyone or just one person on Skype? If it's one person on Skype, they have a bad microphone. If it's everyone, perhaps you need to reconnect your speakers.
If reconnecting the cables doesn't work...you need to figure out if it's only with Skype. Let us know where else it's a problem.