Came across a new one yesterday. While trying to use wireless mics in a particular room, the AF was pegged (note the yellow LED), moving to the hallway corrected the issue. Took a while to figure out it was the ultrasonic occupancy sensor in the ceiling. Simply lifting the ceiling tile and placing it above another tile solved the problem. With the help of the facilities guy, he was able to unplug the ceiling-mounted white noise generators too. That's why you show up early to the gig. Happy egg hunting!
Thanks, Steve. We have seen reports of people forced to work in rooms with these things where they couldn't be disabled. Two workarounds were something to cover the transducer like a big felt hat or a pillow (held up with a C-stand). Or else using microphones that are not sensitive to ultrasound (like old dynamic mics, etc.)
As if we weren't already having to deal with shrinking RF spectrum and increased interference. Now we have acoustic interference as well.