Mystery sound
 

A very strange phenomena has occurred the last two times my wife and I have been out in our 2008 15T HiLo. As we've laid down at night to go to sleep, we've heard what sounded like booms in the distant night. These occurred in irregular intervals of between 3-8 minutes. Initially, I thought they were the sounds of someone shooting in the distance, but my wife thought they were coming from somewhere in our trailer. I scoffed at this, but as the sounds continued throughout the night, I began to have my doubts. The sounds continued, though somewhat more muted than initially, throughout the night, and in the morning, I was able to determine that, indeed, the trailer was the source of the sounds. Because of the muted nature of the sounds, I was unable to determine the exact location of their origin, but I am certain they were coming from the trailer. The best way to describe them is that they sound similar to the way a fireworks show sounds from far off, almost as if there is an expansion of some kind within a system. I know this is vague and sounds strange, but I am flummoxed and am hoping that someone might be able to give me a clue.

Was the refrigerator on gas mode
The refrigerator cycling might be it with the burner igniting

It does sound like maybe it's the water heater igniting...water pump engaging? Just a thought.

vague description, but I also think it is the water heater cycling. The cooling/heating of the tank will cause a "KA-THUNK.

Next time out, don't fire up the water heater and see if sound continues. If it is not the water heater also turn off the gas in fridge and run on elect.

I don't believe that the fridge would make that sound unless needs serious work.

Related issue?
 

First of all, thank you all for your responses. Because we were in bed for the night each time this occurred, both the water heater and water pump were turned off when the sounds occurred. However, another problem occurred during the trip that (perhaps?) may be related. While we were using the water (I think hot H2O), a series of three beeps occurred and the refrigerator shut off. Subsequently, each time we turned on the water with the water pump on, the lights dimmed and the lights on the fridge shut off briefly before coming back on. I'm going to replace the water pump (as soon as I can determine the updated model) and hopefully solve that problem. It hadn't occurred to me that the two were related, as the system was off while the sounds occurred. The propane supply to the fridge was connected, though. Any thoughts?

my first thought maybe the camper, like a house, was destressing. The steel, aluminum and wood heat, expand during the day then cool and contract at different rates at night, and, like an earthquake, eventually something gives and moves slightly making a crack, but not so much like a firework in the distance.
Water heater flaming up is a boom, then burn sound, but that would be obvious in the quiet of night, and would not fire up but once in many hours if not being used.
The clicking is the piezo ignitor sparking as the propane is released for the burner to light. It will click click click until a flame heats up the sensor telling it to stop clicking.
If your fridge has the ability to turn on and off the gas, then this would be the same, only much quieter, likely what you are hearing at night but it is not loud enough to hear in the day. My fridge just stays lit the whole time as it is 1997 age, so only clicks at initial light up.
If your fridge is able to maintain a temp then maybe it lights on its own, if fridge had just a dial setting that only controls the strength of the flame then it does not sense the temp and stays lit freezing your fruit and eggs on the cold night.

when you raised the camper top did the lock click in place. It's a long shot but if not locking when top is raised it may be slowly lowering just a tiny 1/32 or so and causing a noise as it drops. this could be a dangerously serious problem if so. maybe hydraulic fluid is low and lock is not engaging it could be dangerous. Just a long shot possibility worth considering as you safety is involved.

Just a thought
 

If you are camping and plugged into 30amp electric run the ref. on electric. Save the propane.