Why is there so much water going into my fridge drip pan?

A leak under my fridge started a few days ago. everything on the net says that its a clogged freezer drain which I have checked and is clear. next the net said to check the seal which is also fine. I have no ice maker so no water flow to the fridge but over night the drip pan has a lot of water in it causing it to eventually overflow into the floor. we don't open the doors all that often and its not humid in our house, what keeps causing this this?