Well space would not be entirely sound free. Things bouncing off your hull. Weapons impacts. Even the roar of an engine that passes close enough to react with your hull. But ctishman is correct, its been the long standing tradition in all space sims that sound is computer generated, based on sensor reading.

Now for my sugestion. Planitary sound tracks. Most planets give off radio waves at some level naturely, even before man the earths magnetosphere reacting with solar activity produces measureable raio waves. Once brought to a freaquency humans can here its accually quite amazing. This effect was accualy used in 2001 a space odisy, though it was accualy Satturn not Jupiter you hear in the backgound.

The Cassini-Huygens mission just retured a new collection of radio data. The story and sounds can be found here http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=589 It would be very cool to introduce accual radio data from our very own solar system into the backgoround around planets, comets, stars, or anomalies.

I am sure much more data from other probes is publicly available somewere. I acculy own a CD with recording of Jupiter and Satturn. I often listen to it when I need to consintrate or just want to relax.