It may be some sort of military radar, but it is normal to hear the beeps in the headset when parked close to the rotating radar antenna. Can you not hear anything at all in that situation?
Yes I've had the beeping in ANR headsets at Cherburg.
Delayed my departure for a minute while I tried to figure out what was causing the beeping! Figured it was easier to solve on the ground than in the air. After checking everything that I could thinking, I looked outside while thinking and noticed that the timing matched the radar rotation :)
Maybe shielding your regulator inside an Isothermal bag (those that are lined up with Aluminium) would help?
