I've discovered, after having bio-wheels on 3 of my tanks, they ARE supposed to move freely initially. They do not start the hesitant movement until they are fully colonised. If they are not moving freely initially, one wants to take care of that, as they may not move at all once they are colonised (the build-up affects the free movement; if its initially impaired it can make it impossible for the water flow to move the wheel).
As I said before, I had a prob with one of my bio-wheels. Was on my 2 wheel Emperor 400; one would spin easily, the other would stop n start. When I called Marineland to find out why (I had switched wheels, and only the right one would stick...didn't make a diff which wheel was in it), I discovered the fact there are those little plastic bearings in there, and there should be one on each side. I was missing one, and replacing it made all the difference in the world. It now moves freely and smoothly.