Has anyone had "ringing" with multiple RGPC units?

After having a wonderful experience with a Richard Gray 400 MKII power conditioner, I added an RGPC 1200 to my system. While experimenting with different ways to connect everything I found that when connecting my DVD/CD player to one side of the 1200 and my preamp/processor to the other half (or to the 400 MKII), the system seemed to ring, which sounded unnatural to me. It sounds more natural with both units plugged into one side of the 1200, or both into the 400 MKII. Has anyone else experienced this? Is this normal? Does anyone know why this occurs? I would appreciate any help anyone could provide.