At the SIGGRAPH 2011 Conference researchers of the Cornell University are demonstrating a new technology to artificially generate sounds of colliding objects. The basis of this technology is to give parameters to each material, which in the case of colliding will automaticly create particular sounds.
Such kind of creating synthetic sounds is something researchers seem to work on hard. Formerly and also at SIGGRAPH a technology called Harmonic Fluids has been introduced, which associates sound to an object with the succeedings that the sound becomes scalable while one is narrowing to or removing from an object. At all such technologies will lead to more realistic environments for example in virtual reality worlds.