I am positive that is the same sound I have been chasing. At home we have narrrowed it down to my cell phone (GSM) and my wifes cell phone (non GSM). With either phone on the nightstand the clock radio which is plugged in but turned off will randomly generate that same sound (although it does seem to occur after I enter a deep sleep and last just long enough for me to wake up and move the phone).
Here is another great data point for you. We have also experienced this sound when I left my phone on the table in our popup camper next to a different clock/radio. No wireless PC networks, no cell towers close enough for reception and very few other campers.
I am positive based on months of experimenting that cellular transmiters are involved in these events. The noise appears to be random but right now I am suspecting that the phone is going into some pulse high power TX cycle.
We have not experienced these events in our church yet but I will be watching this thread closely for your progress.