Hum coming from setup of Phon pre and turntable

Ideas? All other units (amp, pre, cd transport, etc are quiet.) Hooked up my Oracle TT the other day with new Phone pre-Conrad Johnson--when phono is on--loud hum coming through speakers- chassis on TT is grounded to phone pre--

Thoughts---I have eliminated all power cords "grounding" pin with adapter as suggested. No improvement.

Thanks-((I realize this can be very complicated.--but I thought someone might have a checklist from start to wherever--thanks--