It can be a number of things, temperature can play a big role as metal contracts and expands, and viscosity of e liquid changes with temperature too. Even pressure in the tank can cause a leak. All of my bottom coil clearo's gurgled, some worse than others but all of them have done it many many times.
At first I used to disassemble and blow the excess juice out of the wick, then I discovered that by holding it upside down (drip tip down) the excess would also find it's way out of the top where I would be waiting with a paper towel, still not practical though.
I developed a little technique until I moved onto rebuildables to still get a vape, use the excess liquid up, and fix the gurgling without taking anything apart, although it took a few times of getting juice in my mouth until I clocked it.
When taking a draw I would tip the whole thing upside down while I was vaping, so the excess juice would run away from the wick and coil and down toward your mouth, allowing you to dry the wick a little bit and get some vape. The trick is though, is to be quick enough but take a long enough draw to not get liquid in your mouth as well as not burn the wick, if you do this 3 or 4 times you'll find the gurgles gone.
It's due to too much juice around the coil and wick that it blocks the main air hole, by doing this you're eliminating the excess juice from the wick and drying the wick out again, so as it runs back down toward the coil after you've taken a hit and stopped holding it upside down, it will quickly saturate the wick again, and like I said just repeat until the gurgles gone!