Bats use SONAR as they can't see(we think it ,but it's not true,they see very very little in dark) and use echolocation as a technic to navigate.But there are some kinds of bats which actually do have big eyes to see even in nights.(and really big eyes).
Normally bats use larynx to produce the the sound and emit the waves from mouth, but "Horseshoe bats and Old World leaf-nosed bats emits their echolocation calls through nostrils "
So as it seems the makers have imagined that there must be bats which can emit the waves from there ears( tough they use ears as a organ to receive the reflected waves ).This may be a possible answer.
And the pokedex says Noivern:"The ultrasonic waves it emits from its ears can reduce a large boulder to pebbles. It swoops out of the dark to attack."It seems Noivern uses the ultrasonic waves to attack and it can't echolocate with that powerful waves which turn large boulder into pebbles.
Noibat: "They live in pitch-black caves. Their enormous ears can emit ultrasonic waves of 200,000 hertz."
So it seems that the organ which creates the vibration is located within their ears.
This may be the inspiration of Noivern or Noibat: