What exactly do you mean by wobble?
The Powertec is quite a strong rack, been around for a while.
All I can think of is that your floor may not completely flat, so when the rack is ridgid, it may wobble.
If so, you can pack up a corner so it sits totally flat.
If your floor is flat, the only other thing I can think of is that you may not have the bolts tightened all the way, they have to be done up really hard so the metal post tubing starts to crush a bit.
Still, most racks will have a little bit of wobble when you push them in certain ways, doen not mean they are going to fall over and fail when used for their intended purpose.