If you have Park Assist engaged you will hear them. The button is on the dash on the left side of the steering wheel. The Green "P" is lit on the dash when it is engaged.
It's an optional equipment, so if it's not there, it's not there.I checked the manual, looked for the button and the sensors. I don't have them. I bought the car used, so never had the choice to add the option. I have the nav, BT and back up camera but not the proximity sensors. There is no button above the trunk and fuel hatch buttons.