I tried placing a mud brick slab on top of another one, and it became a full block. then I noticed, there was no sound when doing so.

What I expected to happen was...:
There would be a sound for making the slabs into a full block

What actually happened was...:
There was no sound.

Steps to Reproduce:

1. Get 2 Mud Brick Slabs
2. Place one wherever you want, you'll hear the sound then.
3. Place The other slab on top of it, It will then become a full block, notice that there is no sound once the 2 slabs become a full block.