Was out of town last week so am just getting back to this. I have tightened up the belts more and the shaking has seem to resolved itself. Top of the Z tower shakes a little bit but I suspect that is normal.
I drew several shapes and curves on a test piece, but by large rectangle is off square by quite a bit. The one picture shows the measured dimensions (to my best estimate on the corner that did not get drawn). The dashed lines are the orientation of the middle y rails to the outer y rails (see previous post by me). The out of square matches the direction of the non parallel middle rails if that makes sense.