Controversial & Contradictive
It monitors the resistance of the circuit, and if it exceeds a certain level it'll activate the warning. Have a play with the bulb and make sure it's sitting tight in the holder, it could be a loose fitting and the vibrations are causing it to lose contact every so often.
53 A4 2.5TDi Quattro Sport 180 Tiptronic. Heated Buffalino leather, DVD Sat Nav RNS-E, TV, Bluetooth, 6 cd, BOSE, Colour DIS, Cruise Control, Auto lights and mirrors, Interior light pack, Heated mirrors.