[@GummyCat]
The lowest rank he can be is Major. State Alchemists start at that rank due to simply being a State Alchemist.
Also, Alchemy can't just vibrate the air. Alchemy is about rearranging molecules to produce a desired effect in a sense. Such as rearranging an iron bar into a iron sword, or even steel if you have something like graphite for the carbon nearby. It doesn't provide a constant interaction. It can move the air molecules once, but not for several moments at a time if it was constantly active. As far as I am aware after watching the show several times.