When moving in an x/z direction while falling through an air block that contains certain blocks (all 3 variants of torch (normal, redstone, soul fire), lever and tripwire hook with my testing), the walking sound is played (I think the sound when walking across stone).

This can be when falling even just 1 block down a ledge. The sound also plays when jumping up a block. Either on the floor, or on the side of the block, if there is a torch (all 3), lever or tripwire hook. 

The player must be moving in the direction parallel to the wall at the same time.

To reproduce:

Method 1: (Picture 1) Create a wall, with torches (any of the 3), levers and or tripwire hooks on the side of the blocks. Then fall through the blocks while having momentum parallel to the wall to produce the walking sound. (Video Part 1)

Method 2.1: (Picture 2) Create two flat planes, one 1 block higher than the other. Make these out of a block which produces a walking sound different to stone e.g. grass, dirt. Place a torch (any of the 3), lever or tripwire hook on the side of a higher block, or on the floor of a lower block. Then walk at least a 45 degree angle to the wall, and jump up or down the ledge. You should hear the sound of the block you are walking on (dirt, grass etc), but hear the sound of walking on stone when falling down or up. (Video Part 2)

Method 2.2: With the same setup as Method 2.1, walk along the edge of the higher blocks parallel to the edge, with the player's hitbox at least half off the edge of the block. No walking sound should play when walking along the blocks, but you should hear the sound of walking on stone while walking ** 'above' the torch/lever/tripwire hook. (Video Part 3)

-For Method 2.1 & 2.2, the torch etc can be on the side of the block, or on the floor of the lower block (Picture 3)

Note: Video is 360p low resolution to fit within 10MB attachment size