X Axis Moving Axially

Good evening. This problem is not attributed to Linux, so perhaps it doesn't belong here. That said, I know that many of you deal with cnc machines more than I do, so perhaps you can offer some insight.

To put it as best I can describe: my cnc machine has begun moving laterally in the x-axis. If I move the axis all the way to one side, it will 'bottom out' the motor shaft + threaded rod (all moving together as expected) and then advance the axis as expected. Reversing the direction then physically moves my motor shaft through the motor until it 'bottoms out' in the other direction, and then moves the axis as expected.

Some thoughts:
1.) The motor <-> threaded rod connection is tight, and is not slipping.
2.) I do not know what is stopping the axis moving farther laterally. I didn't actually investigate this because I just assumed it shouldn't be happening.
3.) My machine has never had this issue in the past, and since its appeared it has not went away.
4.) I recently installed a laser onto my machine, which is cantilevered out in front of the spindle. I have not removed the entire x-axis assembly to see how the axis behaves under no load, but I have some theory that by adding the cantilever laser attachment that I have introduced extra forces on the axis, creating drag, to the point where it is acting the way it is now. You can see some before and after pictures of the laser addition here (www.instructables.com/id/Add-Laser-Etchi...ities-to-a-CnC-Mill/). By my estimation, the laser + 3d printed pieces are adding a negligible moment to the x-axis linear rods, but perhaps I am mistaken here?

Some troubleshooting steps I have done (some of these might make you scratch your head..please bear with me):
A.) I swapped the X and Y axis motors; no change to the system.
B.) I replaced the x-axis anti-backlash nut, spring, etc; no change to system.

Here are two videos I took of the x-axis moving back and forth. The first is a close up of the x axis motor shaft + coupling + threaded rod. The second shows more of the x-axis, with the spindle+laser housing moving erratically.
drive.google.com/open?id=0BxvIwwO_l8EnM1dydEdTUGpjOW8
drive.google.com/open?id=0BxvIwwO_l8Enb3NSUS13VDZrZW8

Thanks for any help, I'm open to suggestions, repairs to try, etc.

The bearing that holds that leadscrew in place is either lose or having some other sort of trouble. Remove the motor and coupler then investigate the bearing block. You can probably just grab the leadscrew and push/pull it by hand and feel the free play.

Thanks for the tip!

I pulled the motor and was able to pull the x-axis by hand like you said. I disassembled the gantry and replaced the bearing on each side. Overall the old bearings seemed ok, and there was a small amount of wear grease, but nothing excessive. Anyway with new bearings in place I put it back together and attained the same results, where I could push / pull the x-axis about a quarter inch or so. (Basically no change...) I measured as accurately as I could the linear movement and then disassembled one side of the gantry and added spacers (in this case washers) next to the bearing. I erred on the side of "slightly to thick", and then put everything back together.

Having done that I was able to get repeatable results with my machine again, something I haven't had in quite a while, so thanks for your advice.

If you're ever in town I owe you a drink!