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Yes the item against the louvers can cause problems
Another thing to check is the door seal even on the bottom this will let moisture in that will accumulate on the colder items
I think what Glenn means is the drain pan under the evaporator coil in the freezer section. That pan has a tube that leads to the drain pan on the bottom, where the water evaporates away.
You need to remove the back cover of the freezer section and you will see the coil and the pan below the coil. The drain pan is very likely iced up, so you'll need to defrost it with a hair dryer and then try pouring warm water in the drain pan to see if it drains. If not, there still could be some hidden ice in the drain tube or it may be clogged with something else.
If several tries with the warm water doesn't work, you'll need an air tank to blow through the tube (sometimes it's easier to blow from the bottom of the tube back up).
Let us know if that helps,
p.s. If that works, please accept Glenn's answer rather than mine since he was on the right track before I butted in. ;-)