When stepping down into to a 1 x 1 block wide hole, as I pass over the edge of the hole I hear a damage tick and receive about half a heart of damage. This is not fall damage when I land, this is occurring at the top of the hole.

Sometimes you do not even need to fall through the hole, just walking around the edge of the hole will do this as well.
Most consistently repeatable when a trapdoor is used at the top of the hole.

It only seems to appear when it is 1 x 1 block wide with a fall of about 5 or more empty blocks underneath.

Also, when walking backwards and placing blocks repeatedly in a 1 block deep trench, if there are torches on the inside walls of the 1 block deep trench you will again hear the damage tick and take about a half heart of damage when you pass by/though the torch.