My 2018 13" MacBook Pro makes creaking/cracking noises when slight pressure is applied to the palm rest area, to the bottom, and when the trackpad is force clicked.

Does the Bottom Case appear to fit properly all around the edges? It should be a smooth transition to the Top Case.

There are four snaps to hold the Bottom Case to the Top Case frame. The two outermost snaps are very strong/tight and sometimes difficult to snap in place. The other two snaps are much weaker and are located about 1/3 from each side. All snaps are roughly halfway between the front to back.

Open the display on the laptop and turn the laptop upside down placing the laptop keyboard flat on a table with the display overhanging the edge of the table to keep it safe. Then try pressing on the bottom case of the laptop about an inch from either side about halfway front/back. Press firmly to see if the snaps are loose and will lock into place (it will make a loud "pop" sound if they were loose). Then try pressing more gently about 1/3 of the way from either edge (right/left) to see if those center snaps are loose (these center snaps will just make a quiet sound if loose).

I'm not sure what it could be. I have been hearing a popping sound from numerous MBPro 2016+ laptops without anyone touching them. The sounds happen so suddenly and are so random and rare that we haven't been able to discover the source. I wonder if this could be related. I wonder if the noise could be coming from the Trackpad. I know it can make clicking sounds.

If you can reproduce the issue at will, then maybe you can put your ear to the laptop to see if you can narrow down where the sound is coming from. Maybe you can even make a simple stethoscope. I've used screw drivers or small pieces of wood held with one hand cupped at the end so that the sound transmits through the screwdriver/wood and by cupping my hand it acts like the cone on an old Victrola so you can press you ear against the cupped hand to hear the noise. The more solid the item/stick the better. It is an old trick my Dad taught me when working on cars to find the source of a particular noise in an engine. Just make sure you don't use anything that will scratch or damage the laptop.