When i get ultrasound or doppler at the hospital in labor/delivery e.r. my baby goes nuts in my belly. why? can he feel it vibrating or maybe hear it?

Sound: Imagine if you were in a pool of water and someone put a waterproof speaker up to the pool's edge. Definitely the babies react to the sound of the doppler, but, i don't think there's any evidence that they respond to the vibrations of the sound waves like a dolphin, the waves are just too far apart for that. That's great though! the nurses don't have to use an acoustic stimulator !