] The check made by the crew found no changes either
] in the equipment section or the atmosphere of the
] station, which would have changed instantly if the
] station's skin were punctured, Gorbunov said.
]
] The sound might have come from some of the
] station's equipment, not a collision, he said.
] However, a spokesman for the Russian Space
] Forces, which focus on monitoring the Russian satellite
] fleet but also keep track of the space station, said the
] station collided with a piece of space junk.

Orbital debris is a hazard that we have yet to truly address or contend with in LEO as of this time - it will be interesting to see how this pans out. Speculating that orbital debris was the cause of the mysterious crunch, it would have to be moving at a very low relative speed NOT to cause a catastrophe.