I work at a bar/music venue. The computer is plugged into a mixer that plays to the back of house (powered speakers). Those speakers are plugged into sockets in the ceiling (power). We just hooked up a thunderbolt to hdmi to a hdmi splitter(4way). The hdmi cable going to the splitter is 35ft. The splitter And 4 tv's And 4 cable boxes are plugged into the same sockets in the overhead. And a hum is coming from the powered speakers when the hdmi cable is plugged in to the splitter. I assume we have a ground issue and need an electrician... But I'm hoping there might be an easier fix?