maybe... gremlins? 8)
joke aside... when i play facing my laptop (actually a portable workstation HP8770W) tweakin on AnxeEdit or CabLab I get every kind of interferences in my sound (SC, HB, whatever). The screen monitor, the hdd, even the DVD drive. It's easy to quite that simply turning myself away from the laptop just half step.
Your church (btw... OMG! Woodstock wasn't so full of gears!!!... nor the MUSE live!!! ) have tons of waves flowing everywhere (step-motorized lights, screens, radio-signals, hi-power led lights) and I see that many things are on the stage floor just near the band.
Anyway... as Cliff said... Occam's razor: check cables (even where they runs on the floor maybe crossing something noisy like dimmer boxes, DMI cables etc...), check connections to the board or the snakebox (AND connections from the snakebox to the board!!! I had experiences about that!).