Citroen C4 ringing/sirin sound coming from boot

I have a sirin/ringing sound coming from some electric cables inside a vent type opening in my boot, located to the right hand side wall. It will not stop even when the ignition is off, so Ive had to disconnect the battery to prevent it draining my battery. I have a tow bar connection that thh flap snapped off the electric connector, and have had extremely wet weather. Could this have gotten damp and causing it too sound. It suddenly started when I switched my head lights on however I was not connected to tow at the time.