Not everyone has the same hearing range (it tends to get worse as you get older, hence those ultrasonic teenager repellers that people claim are for cats). If a device is running at the very low end of what we consider ultrasound and OP can hear higher than most then maybe they can hear the sensors. I would be surprised if an ultrasonic sensor was running this low though.
People often believe they are hearing ultrasound, but instead are hearing clicking noise or sub-frequencies emitted from the capsule that are not actually part of the ultrasound.
Not everyone has the same hearing range (it tends to get worse as you get older, hence those ultrasonic teenager repellers that people claim are for cats). If a device is running at the very low end of what we consider ultrasound and OP can hear higher than most then maybe they can hear the sensors. I would be surprised if an ultrasonic sensor was running this low though.
People often believe they are hearing ultrasound, but instead are hearing clicking noise or sub-frequencies emitted from the capsule that are not actually part of the ultrasound.