Tracking question

Hello! - I am trying to hunt down the source of some low head speed vibration and I think I may have found something. When the head is spinning at LOW speed (maybe 1/4 throttle) it appears that the tracking is off. ( the blades appear "Split" when I eye them). When in the air, the blades appear to be tracking just fine. Is that normal? Not sure how to solve for that or if that is just the way it is......

Thanks for your help!