I think that the cracking or snaping sound heard in the video was the concrete driveway suddenly failing under the rear outriggers of the crane. In the second video, in several of the frames it looks like the driveway is crushed under the outriggers. It's hard to see because unfortunatly there is a big damn cardboard box in the way. As the load was moved farther away from the crane the load on the rear outriggers would constantly increase until the, typically, thin concrete of the driveway suddenly failed. This sudden "lurch" could then have initiated the tipping over of the crane.