When my trailer is unplugged from shore power (which is very, very seldom), and the house battery gets depleted, the power converter chirps. As the battery gets lower and lower, it chirps more and more. The fastest I've heard it chirp is about once ever 15 seconds.
When I finally figured out it was the converter chirping, I couldn't figure why? I explored the trailer, inside and out, just to find out I had unplugged the camper from the power source when I mowed the grass (at home) to pull the cord out of the way. After mowing, I strung the cord back, BUT didn't plug it back in the wall (This was before I had my 30 amp connection installed). After a couple weeks sitting, the battery ran down low enough to cause the converter module to begin chirping. DUH! I plugged the camper back in and .... really .... it's never chirped again!