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That is usually a sign that the drain hole in the bottom of the unit is plugged up and allowing the water to fill the trough and overflow into the opening. You have to take the cover off on top and get to the drain. Not sure if that is a job you want to tackle, but if so, I can direct you once you get it off. I will make a phone chat offer for you as well. Many customers prefer this method of communication. All follow ups are included in our fee.
Just checking back to see if you were able to get that checked out? IF you need more assistance on getting that upplugged let me know.