Hi everyone... I was setting up our stage for the last choir concert of the year. When they built our stage, they put in hanging microphone jacks on the ceiling.... three down and three up. The sound package that we got included four hanging microphones. They hung two down and two up. The problem... the four microphones were hung literally 1' in from each wing, leaving the entire center of the stage uncovered by the mics' patterns. I decided to move them in more to better mic the choir. Our TD was AOL, so I had our stage manager, who is more of a "jack of all trades" type of individual, go up in the lift and uncoil the zip-tied extra of each microphone and move them towards the center. He did so to one and we had an awful ground hum. Here is what he did... He wrapped the microphone around one of our teaser batons (which are just schedule 40 pipe). I tried everything and still the hum was terrible (you couldn't hear anything other than it). Thinking... "GREAT... the concert is in a half an hour... what can I do?"... I remembered comments made in earlier posts about possible ground loops causing this hum. I told him to take the microphone off of the baton and use the conduit that was run to the mic jack to hang it because it was probably grounded whilst the schedule 40 wasn't. He did and the hum was gone. Thanks again to the brilliant minds at CB.