Skoda Octavia parking sensors not working

Ok so I've just brought an skoda octavia 1.6fsi but i had a few faults with it one is the parking sensors that don't work, when i turn the key i get a few bongs is this normal? When i engage reverse i get a lower bong noise (i thought this was normal on the test drive as my saab made a noise when i engaged the parking sensors) but reading the manual it says there shouldn't be any bongs when engaging reverse and that if you hear a noise there's a fault. Also there's no picture of the car on the dash when in reverse that only comes for a split second when you change gear, i might add the reverse lights cone on and the car reverses ok.