My mate has a few problems with his a4.
Firstly the central locking has a mind of its own and is constantly unlocking the car when driving, theres the odd time the boot opens on its own too. The glow plug, esp and abs lights come on too. I hooked my vcds lite upto it and there was 11 faults in the central conveniance unit which i cleared and 6 came back, and it says the brake light switch is faulty, but we replaced that about a year ago and the brake lights are working fine. Ive had a bit of a search and it says about water getting in under the scuttle panel and damaging the electrics there and also about water getting into the passenger footwell and damaging the central convenience unit, but they are both dry as a bone with no signs of any water that has got in.