What's going on in my fermentor?

I am doing a 1 gal hard lemonade experiment and I am getting some weird activity in my airlock. I am using a 3 piece airlock and when I plug my airlock in, some of the water is getting drawn up under the inner cup. From what I've read here this is referred to as suck back but what I can't figure out is what is causing this. Anyone have any ideas?

Temperature differential between contents and liquid in the airlock. Try cooler water in the airlock

Most likely, the wort temperature was significantly higher than your fermentation temperature at the time of sealing the vessel. As your wort cooled, the liquid and air that you sealed inside the fermenter shrank a little bit. This creates a lower air pressure inside the fermenter than outside, which causes the airlock water to be drawn up into the inner cup. As long as it's not sucking it all the way into the fermenter, you're fine to leave it the way it is because soon the yeast will start their activity, create CO2 and other gas, and your pressure differential will go in the other direction, at which point it will start bubbling.

Thank's guys I'll keep an eye on it and see what happens.