As lame as this is, I think sound could really function well in the game.

It would be super effective against:
Steel
Ground
Water
Flying
(Because all of these carry sound waves sort of)
Weak against:
Rock
Bug
It would resist:
Water
Steel
Ground
Fire
And would be weak to:
Bug
Rock

I would retrofit the typing onto a lot of pokemon, (Whismur line in particular, Meloetta, perhaps Milotic), as sound based moves are actually really common.

Some potential issues I could forsee would be with the ability liquid voice and the movie Hyper Voice for Pixilate pokemon.

Thoughts on my idea? Add your own?