Any Soundboard Techs Here?

Any live mic is picking up sound. It might be a voice, an instrument or just ambient sound but if the mic is live it is picking up sound that goes to the mixer. In that sound mix is also the amplified sound of what was intended to be picked up.

Say you have the pulpit mic in use by the pastor. That is the intended input you want sent through the mixer, the amp and out to the speakers. If you keep the other mics open, all of them will pick up what they get from the speakers even if it does not create feedback. Every mic has a polar pattern which is the shape of the area the particular mic is designed to hear. Depending what you have for mics and where they are set you should anticipate patterns from some of the mics overlapping each other.

Short answer is your sound person is creating mud. The output will be distorted even if it doesn't seem to sound so.

Do a sound check with the room at full of people. The sound person should be able to use a piece of tape along side the potentiometer (pot) for the appropriate level when that mic is in use. When it is not the level can be pulled down to zero (muted) and back up to the needed level when the mic is needed again.

I worked at a radio station several years ago. We had a very nice ribbon mic in the production room. I was doing a voice over and could hear a clicking noise in my headphones. I checked all the connections, the board, grounds and stuff and couldn't locate the source of the clicking noise. I finally found it. The mic was sensitive enough to pick up the relays on the gas furnace through the duct work into the studio. It was highly unlikely that anyone would ever hear the clicks underneath all the other sound in the piece BUT I knew it would be there.

Information on mics

Information on board operations