Parking Sensors

[Rockfiend]

B6 Estate with OE parking sensors. When selecting reverse, more often than not, there is a high pitch tone ( not the front or rear sensor tone), the parking sensor switch flashes and the radio display goes on/off. Thought it might be reverse light switch, but it was doing it today whilst stationary and not in gear. Havent had a chance to vagcom it for any current codes. Any ideas where to start?

Any pointers greatly appreciated

Passat B6 Highline Estate 2009,CBAB, RCD310