That's not good at all - sounds like something's definitely wrong with it. Have you cleaned out the impeller well & area? It could be something preventing it from turning properly.
This is a silly question, but are you putting the handle down, waiting 2 minutes, giving the filter time to fill up with water/expel air before you plug the filter in again after maintenance? If the handle isn't down properly or the filter's full of air, this might cause a problem.
Have you checked all the hoses, connections, intake, spraybar for clogs? My FilStar sometimes gets leaves stuck in the wierdest places - enough stuff wodged into one of the tubes/hoses could cause a problem without completely disrupting flow.
I can't think of anything else, sorry if none of that's helpful.