Periodically, my batch (1-gallon batches) will seep and bubble through the top of the airlock after I've transferred it from the primary to the secondary. My typical process is to transfer from primary to secondary when the SG reaches 1.03-1.04. And as a result, sometimes when I check on it the next morning I find a mess that has seeped out the top of the airlock and has run down the outside of the jug and also has splattered on the adjacent wall. It happens about one out of every four batches (as an estimate), but my process is fairly the same each time. Do I need to let the SG drop further? Or, is something else causing this that I'm not accounting for in my initial steps.