I had a theory that it was someone walking across the field with an electronic device, like a flashlight. So I looked up the duration of the signal, size of the field, and average walking pace. It matched perfectly.
They finally traced it to people using the microwave in the break room in a very specific way. Some people liked to open the microwave door before the timer went off. The microwave stopped, of course, but there was a split second where it was still emitting while the protective cage was opened, and the energy that leaked out during those couple of ms were enough to screw with the observatory equipment.
Aliens? Nope, just some tired grad student reheating their coffee.