Rebuilding terribly engineered laser cutter

[threedee]

X is behaving on its own. I did multiple different scan engravings with no adverse effects. No vibration until Y axis engages. If it is only used to move a scanline it doesnt show at all. But try to cut vectors - bang, vibration all over the travel path...

Also, i have checked mirrors for wobbling/rattle - everything is tight and screwed down. All the way along the beam path, from lens to tube itself...