Crackling or popping noise heard inside the hull; beneath the surface

We often hear it in Australia as well.
I also sometimes hear it SCUBA diving, between the noise off breathing.
We are not floating on "dead water" thankfully! there is a whole universe populated by many thousands of creatures making a noise, whether they are fish crushing on coral, shrimp feeding, mussels or fish. The noises might be coming from miles away and are amplified by the water and void of the hull.
It must go on all day, it's just at night the WE are quiet and can hear them. Kind of like not being able to see the stars in the city, but then seeing a night sky while far away from human made light.

I know EXACTLY what causes that noise!!!!!!!!!!!!!!!!!!!!!!!!!!!!

It's the Rice Krispee elves when they go scuba diving........snap, crackle, pop!!!!!!!!!!!!

I would say that Palm Beach ICW gets pretty brackish on the outgoing tide. Over in the Abaco's and Exumas, wood pilings that are a decade old have NO worm eaten activity. Same with barnacles, you just don't get them in the Exumas.......I think because the saltwater has too high of a salt content.......

Here's my SWAG (scientific wild ars guess),
It's not from any living creatures against your hull. Sound travels through water. The boat is acting like an ear, with the hull like an ear drum getting hit with the sound waves that are then transmitted to the boat. Sounds can be from sea creatures, other boats, water discharge, etc that may not be in the immediate area.
I'm no scientist, but I did stay in a Holiday Inn last night (reference to a funny tv commercial for my non-US friends).

There are several sites online with training materials for US Navy sonar operators. They have recordings of "biologicals" and other sound sources commonly heard on shipboard sonars and through the "sonobouys" used to locate submarines.

Snapping shrimp noise is a favorite training sound because of its properties.

It happens in fresh water also ! My guess is small fish eating insect larvae /aquatic organisms off boat bottoms and pileings. I have observed and heard fresh water drum (sheephead ) grazing on zebra mussels on sheet pileing