Intermittent, random, loud popping noises.

With just the speakers hooked up to receiver, no antennas or input devices, volume set at minimum, system makes loud popping noises. Also, whenever I press any control button on the front it makes a loud clicking sound through the speakers a minimum volume. I work in a hotel and whenever we use wireless mics there is a loud popping noise. I have tried to use different mics, different mic cords, new mixers, and lifting all the equipment off the floor and nothing happens. The popping is loud and seems independent from any other source do you have any advice to help?