Maybe this is it! Continued HandiQuilter saga...

THIRD carriage arrived today.   #2 carriage was swaybacked and no matter what we did, you could not level the frame because the problem was in the CARRIAGE.   With the machine near the back of the frame, it would roll forward and stop in the middle sometimes swinging back and forth, yet if you rolled the machine to the front and took your hands off, it also rolled to the middle....   Quilted like you were plowing an unturned field.  Imagine my dismay when we set up the 3rd carriage today and she loudly "clicked" all across the tracks...   Good grief, this one had a bad bearing on one of the wheels.   Thankfully, hubby determined which one it was and replaced it from carriage #2.  Customer support said "but I checked it myself"...  but if you don't have the weight of the machine on it, you might not notice a problem and it certainly did not "click" when rolled.   After swapping out one of the wheels, no clicking and the frame was level!  Now, I must get something prepared to see if she quilts...