Ghosting

I think I have read all the forums on ghosting, but I still haven't hit on my problem exactly. I have a mix use boiler,1 zone DHW, 1 zone HW baseboard, 4 zones Radiant floor, each zone has a Taco 007 circulator and BG check valves.It's controled by a SR504 daisey chained to a SR503 taco control and has another 007 circulator on the return of the boiler. I get ghosting on the top radiant zone & sometimes the next one down. I have replaced the check valves on both zones, but did not help.My thought is the return circulator is drawing enough pressure drop to open the check valves. I might add that three radiant zones share the same return(2 ghosts one does not). I came to the conclusion I have two options replace the taco controls with IFC's, having two check valves or put a Hydrotrol HT-34 on the return line.I have been battling this problem for several years and I would much appreciate your input.