Ugh. Thought I was being all smart by zip-tying my audio stuff (mixer, wireless headset receiver, hearing impaired transmitter, Bluetooth receiver) to a board with a power strip on it to power all those things. Turns out having the power supplies close to the transmitter, and having the power cables neatly bundled, causes all sorts of noise. And that unbundled, my Landmark transmitter is actually less noisy than the Williams. Need to figure out another configuration for easy setup.