Lately I have noticed that when I move the Z truck up and down (no power) at about the half way point it seems to catch, almost like a detent, put a little more pressure on it and it moves normal again. I took the Z motor off and the catch is still there, actually worse, but with the belt hanging loose inside the truck I cannot tell if it is the loose belt causing the catch or something else. I have lubracated the bearing and all four bearings are tight and rotating. Any ideas?