Puddle of water at bottom of fridge...seems to be leaking out from Freezer tray at top of fridge. Probably plugged line. Can't figure out how to get tray off: there are two screws holding it to bottom of freezer, but how to detach from back of fridge? there is a plastic trough at the top back of fridge that that has plastic plugs (or screw covers) holding it. It looks like the water should go from the tray into the trough and then down a line at back of fridge, but is instead spilling over and collecting on bottom.