My coupler was kind of rattling too, but I was doing some heavy swing on 32 inch blades. It is secure. But I also hung it on my wall horizontally and it 'sinks' in the middle. I went back to my old sound coupler for display. The point is it's pretty normal.
Sounds like you need to tighten the female end. As I mentioned above, there's an inner ring that comes loose.
My staff started 'sinking' as well but once I adjusted that part, problem solved