Popping noise at night

[sailorpappy]

My cd 28 is on the hard in a boat yard in coastal Georgia. I'm working on the boat and sleeping aboard in the v-berth at night.
A popping noise wakes me from a sound sleep, usually between midnight and 2 a.m.
Can anyone give me a hint as to what might be causing this noise? Nothing is falling onto the boat. No one is banging on it. But it is loud and sounds like it's right next to me.
I've been told that it could be contraction or expansion somewhere on board due to temperature change. If the vent line to the head is clogged, could that be a cause? Could it be the fuel tank contracting? The fuel tank is almost full.
My neighbor's cat sometimes comes visiting, but she lands with a dull thud on the topsides, nothing like the sharp boom that wakes me.
All explanations welcome!

[flyboy5724]

Sounds like your holding tank is not venting good. Check your vent to make sure no insect has made it home. My 28 had a similar situation a year ago.

[sailorpappy]

Thanks flyby. I'm in process of replacing the thru hull and maybe using a hose with larger diameter. There is a lot of corrosion where the thru is secured. So it's time for renewal. Well see if that cures the popping noise.