But, imagine if instead of opening the bottle, you just somehow reduced the pressure then quickly increased it back to what it originally was. The carbonation would go from liquid -> gas -> liquid very quickly. CO2 bubbles would form then collapse.
Converting from liquid to gas is not a special property of CO2. There are liquids in your joints that will convert to gas if you drop the pressure. That's what happens for an instant when you crack your knuckles. What you are hearing is the bubbles of gas collapsing as the gas converts back to liquid.
The time it takes for the bubbles to dissolve again seems to be responsible for the "cool-down" period that you experience between cracks.
Hole theory: hole appears, (no hole before cracking, hole forms after cracking).
However, "hole" is usually used when the empty space goes entirely through the object, whereas a cavity means that there is an end/depth to it. For example, digging a hole in a sand is really also (more accurately) digging a cavity.