New Ground Loop - What Could Have Caused?

I never before had a ground loop in my BR system. Everything, amp, pre, tuner, including Verizon FIOS box and TV, is plugged into a PS Audio Juice Bar, which is plugged into an Audience AR1P plugged into the wall.

Upon returning from vacation, I now find I have a very nasty ground loop I so far have been unable to cure.

What would cause a ground loop when there had never been one before? Thx.

Neal