I'm not sure where to post this. On my FM radio (yes, I am pretty old fashioned), if you tune it to be slightly out of a station or if there is a weak signal or something, you can distinctly here a strange pattern of interference in the background. This consists of a rapid pulsing of white noise at about 100 bpm. As the radio is tuned further from the station, the length and volume of the pulses increase until all the sound is drowned out by static. This is probably reproducible on most radios. Now, I have no idea where this pulsing static comes from, and there seems to be nothing in the visible vicinity that may cause it. (no mobile, computer etc around) So where does it come from?