Ok managed to download the video. Looks like it is the stepper. You can see it stutter in slow motion with the noise you where talking about.
First if you move the gantry by hand make sure it is the same distance from the end of the rail on both sides. Otherwise it could bind. Its unlikely given the video but still worth looking at. It's best for this reason not to move the gantry by hand on the 1000mm xcarve as there can be a bit of play.
If thats all good then do you have a multimeter or know someone who does? You will need one with a continuity tester(Beeps when it has a complete path) on it. If not get a cheap one that does continuity just don't go plugging in a cheep one into any high voltage things.
Unplug the wires from the gshield and put one test lead on the top most screw terminal(AKA the one that holds the wire for the motor) and at the same time just wiggle the wire to make sure it is not lose. Then put one test lead on the wire you just unscrewed from the gshield. If it beeps then that wire is fine. Continue this for all the wires. Any wire that does not beep may be broken or not screwed down enough. The vibrations may have undone one of these connectors at some point.
If that fails to find a fault then try changing the wires on the gshield with another axises wires. To make sure it is not a failing stepper motor driver. You could try this first but if your unplugging everything anyway you may as well test the wires.