Hey John,
as Jim already mentioned, this stuttering can appear on insufficiently squared machine. But it has to be coplanar too.
You have to ensure the machine is both, rectangular (“squared”) and coplanar.
For the first a quick check for rectangularity, you check for identical diagonals with a bar gauge (see link) that you put exactly where the chrome-plated hardened steel hollow shafts come out of the black aluminium extrusion feet. A later, better check, is to program and mill a rectangle with a v-bit around the limits of the workarea and then check the result for identical diagonals.
Note the before doing this identical diagonals check, you should use the bar gauge to also check if the rails between the two feet are identical on left and right! If they are not, the diagonals check would not be done in a parallelogram, but in a trapezoid, and therefore would be useless. The rails have first to have identical length on left and right.
The check for coplanarity is made with the two intersecting fishing lines. Be sure that if they touch each other in the middle, that you have to reverse them so that the other is on the underside and repeat the check if they touch. They have to touch each other in both cases, then the machine tabletop/machine base/QCW frame is coplanar (=all four feet are in one geometrical plane).