A question on another SE site prompted me to search for 'Aircraft engines untrasonic noise dogs', but with not much success. The OP's dog barked like crazy at turboprops, but was not bothered at all by 'louder' noises from light GA planes with piston engines, even when led next to them as the engines ran up on the ground.
Does anyone know how much ultrasonic noise does a small turboprop put out? I suspect that it may be worse, in proportion, to that from the large turbofans on airliners since the hp shaft revs so high on those little engines.
Maybe that noise that is merely an annoyance to humans is actually painful to dogs etc?