In the vacuum of space, sound waves cannot propagate because there is no medium for the waves to travel through. Sound requires a material medium, such as air, water, or a solid, to transfer its energy and create compressions and rarefactions that we perceive as sound.
In the scenario you described, where two rocks collide in the vacuum of space, no sound waves would be generated or transmitted. The rocks would interact with each other through their physical collision and the transfer of momentum, but there would be no audible sound resulting from the collision.
However, it's worth noting that if you were inside a spaceship or wearing a spacesuit and close enough to the rocks when they collided, you might still hear some sound. This would be due to the vibrations being transmitted through the solid structure of the spaceship or your spacesuit and then reaching your ears, rather than the sound waves traveling through the vacuum of space itself.