I have a similar issue. When I plug in the trigger on both or one EP500 I get a hum, once triggers are removed hum goes away tried removing ground screws did not make a difference.

RJ


M100 V4, VP180 V4,QS10s x4 V4 M2 V4 X2 EP500 V4 X 2,ADA 1500-3, ADA1250 - 7 N3