I always wondered the same about ultrasonic parking/proximity sensors on cars.

induction stovetops create extremely loud high pitched noises, some get up to 100+ decibels. You can't "hear" it but at higher heat levels you can definitely "feel" it in your ears.

What cars produce ultrasound? I thought radar is used.

Most cars have ultrasonic sensors for parking and radar for longer range detection, such as cruise control.

Every single car from every manufacturer that has PDC sensors in the bumper, which are typically visible as 4 circular sensors on the surface of the bumper.

Wikipedia says both ultrasonic and electromagnetic are used: https://en.wikipedia.org/wiki/Parking_sensor

One of the references is for a Mercedes system that uses ultrasound

I hear some car alarm sensors when passing by, the ones that will trigger when someone is about to park too close and hit the armed car.

LED bulbs must drive them crazy. Many emit ultrasounds that I can hear when I'm next to such bulbs, like that of a vibrating capacitor (low quality AC filtering, low quality capacitor, or both).